This is Masterpiece Mystery!

It was her word against his, you see.

But they'd had a relationship.

Is that what you'd call it?

All you've got is supposition.

You have motive!

How could I send it?

I was at work.

This is what I want to do till the day they carry me out of here.

Do you love Laura?

(siren blaring) LEWIS: Put it down slowly.

"Inspector Lewis."

I don't want to die.

The final episode, tonight on Masterpiece Mystery!

(thunder) (wailing) (click) WOMAN: "I may not even answer at my trial, "and it seems to me that "there is so much of this strength in me now "that I shall vanquish everything, "all of the suffering, "only so that I may keep saying to myself constantly, "'I am!'

"I may endure a thousand torments, yet I am.

"I may writhe under torture, but I am.

"I may sit in a tower, but I exist.

"I can see the sun, "but even if I cannot see the sun, I know that it exists.

And to know that the sun is there..." "...that is living."

(faint dripping) Fifteen.

Twenty.

It must be my lucky night.

My eyes are tired.

Maybe I should get an audio book.

They don't complain.

They don't get your medication, either.

Or post your letters.

Or see that you do your exercises.

You do bang on, don't you?

♪ ♪ Thanks for the lift.

It's not like it's out of my way.

Still, it's a bit early for you to go in, isn't it?

I like to pull my weight now and then.

This is how the last one began.

(sighs) Call me, will you?

I left early this morning.

You were still asleep.

Just let me know you're okay.

Frank!

Pickup in Wantage.

Again?

Ladies.

(giggling) Morning.

Any mail for me?

Yes, Professor Capstone.

That's great.

Here you are.

Had your hair done?

Yes.

Very chic.

Thank you.

♪ ♪ ♪ ♪ (explosion) Major blast trauma to the head and torso.

Severe lacerations from the shrapnel.

Designed to kill, then, not just maim.

Adam Capstone, 34.

Currently Bridson-Whitereid professor of geometric topology.

Pure maths rather than applied, and not to be confused with topography.

As if.

MADDOX: The secretary confirmed that the parcel arrived in the post this morning.

Find out next of kin and get Family Liaison on to them.

Also, see if anyone was seen hanging around just prior to the explosion.

Whoever did this might have wanted to stick around and admire their handiwork.

Sorry, excuse me, excuse me.

You have to let me through.

Detective Inspector Lewis-- can I help?

I work here.

They said there was some kind of accident.

LEWIS: Would you like to move back, Mr...?

Capstone.

David Capstone.

Are you related to Adam Capstone?

He's my brother.

Would you like to come with me, sir?

LEWIS: How long have you and your brother worked here?

We never really left.

I got a double first at 17, stayed on to do an M.Sc., and then I joined the staff.

Adam was the same, only he got his double first at 16.

Two geniuses in one family.

That's an overused word.

We specialize in knot theory.

Knots have their own theory?

Yeah, there's some of them.

But it's the ones in DNA that we're particularly interested in.

If you can figure out how DNA coils up, how it's packed, then you can unpack it.

Modify it, repair it.

That's what we've been trying to do.

A team.

Any idea who would want to attack you like this?

No.

Our research, if what we've discovered is correct, then we're talking about new ways to fight genetic diseases.

Cancer.

New hope, new life.

Why would anyone want to stop that?

Maybe it was more personal.

Um...

These came.

Adam wanted to get rid of them.

Said it was a crank.

That if we ignored them, they'd go away.

LEWIS: Any idea who sent them?

Mr. Capstone?

Um... Well, there's someone, but I can't believe that she'd... Kate McMurdoch.

And she is...?

She was one of our students.

Got it in her head that she'd made some major discovery.

Accused us of stealing her research.

And had you?

No, God, no.

It's an inflated sense of her own importance, I'm afraid.

We had to let her go, and she wasn't happy.

Open day at the allotments.

Said I'd help on the cake stall.

You haven't got time.

I'll make time.

And the hospice?

The day center?

Checking up on me?

Imagine devoting your entire life to working out how to unravel knots.

Imagine.

Kate McMurdoch is currently on her way to the Cheddar Gorge.

Mountaineering Club; they left this morning.

How long for?

Just for the day.

I'll be waiting for her when she gets back.

REPORTER: An explosion ripped through the prestigious mathematics department at Oxford University earlier today.

Police are treating it as suspicious and believe it to be...

It's up.

Hardly surprising, is it?

REPORTER: With one fatality confirmed, there are at least a dozen people and staff... Wallet, watch, and wedding ring.

You should be able to get a positive ID from those.

Yeah, we'll get them round to his wife.

At least her last memory of him won't be that.

Thanks, love.

Have you got it?

Present for the baby?

No, not yet.

But you suggested it.

Yeah, well, I've been a bit distracted with the bomb going off.

You know how it is.

All that way.

We don't want to turn up empty-handed, do we?

Yeah, I'll get onto it.

I promise.

Yes, that's his.

It has "Always" engraved on the inside, see?

"Occasionally" would've been more accurate.

I want to see him.

LEWIS: That's not a good idea.

We can arrange for someone to visit you, if you'd like.

No need.

And we're going to need access to some of his things.

Of course.

His computer, his phone records, bank accounts... Help yourself.

You won't find anything.

Oh, were you going to give one of these lectures?

We all were.

David, me, Adam.

LEWIS: You're a mathematician too?

No, I'm a chemist.

We do the lectures every year.

Mine are usually demonstrations, chemical reactions, that sort of thing.

Adam's were always more flashy.

"Maths and the Calculus of Coitus" was a good one.

Who knew maths could be such fun, right?

What is the Lockston Foundation?

Donald-- my father.

He bankrolled Adam and David's research.

Adam got to do whatever he liked and Dad picked up the bill.

Oh, can we continue this outside?

I have a lecture to give.

Surely, in the circumstances...

I prefer it.

Keep busy.

Better than being alone.

Not good at that.

Five years we were married.

I should've left him long ago.

God knows he gave me enough reason.

He cheated on you?

Forgive me, but was your husband seeing anybody at the moment?

I don't think so.

I was surprised when he went into work early this morning.

I thought maybe another student.

I tried leaving him three years ago.

February 7, my birthday.

He'd gone to Toronto for a symposium, and I packed my bags.

You waited till he was out of the country?

I've never been very good at confrontation.

But even then, I still took him back.

Hopeless.

I tried hating him, especially after Paula, but that didn't work either.

Hopeless case, really, so... Who's Paula?

Paula Guitteau.

She was one of his students, and they had a thing.

Had?

They never last long, Inspector.

The last time they met, Adam said he wanted to end it.

Two days later, she started yelling rape.

And did your husband rape her?

No, of course he didn't.

I mean, he never denied having sex with her, but it was consensual.

For old times' sake.

And you believed him?

The girl had... issues.

She was unreliable.

So the charges didn't stick, and the case was dropped.

Where can we find this Paula Guitteau?

You can't.

She committed suicide.

MRS. GUITTEAU: Paula loved the garden.

She and Frank used to do it together.

Before Paula died, she went into the garden to pick some flowers-- peonies and forget-me-nots.

And she put them in a vase and she left them here for us.

And she went upstairs.

This was after the rape charges were dropped?

I found her.

She'd used a belt and a hook on the back of the door.

It was her word against his, you see.

She didn't stand a chance.

Not against the maths superstar.

But they'd had a relationship.

Is that what you'd call it?

We're not exciting, Inspector, you know.

We're just ordinary.

To Paula, someone like Adam Capstone must've seemed... She was flattered?

No, she was a child.

All he had to do was click his fingers.

It left her feeling dirty.

She told him that she wanted to end it, so he...

Afterwards, she felt so ashamed.

It took me two days to convince her to tell someone.

"Trust me," I said.

"Tell the truth and everything will be okay."

So it wasn't Adam Capstone who wanted to end the relationship?

No, it was Paula.

She stood up to him and he wouldn't accept it.

So he made her pay.

How did that make you feel?

How do you think?

I wish only bad things for Adam Capstone.

What?

Adam Capstone died this morning, Mrs. Guitteau.

Somebody sent him a bomb in the post.

My God.

Also a number of threatening letters.

Not from me.

What about your husband?

Frank gardens, Inspector.

HATHAWAY: Did Paula have other boyfriends?

MRS. GUITTEAU: She never mentioned any.

Well, there might have been someone.

"Always Remember 060302."

Do those numbers mean anything to you?

What, like a date or something?

6th of March, 2002.

Or the 3rd of June, if you're American.

But that'd still make her only about seven.

Sorry, no.

Do you mind if...?

Kate McMurdoch?

DS Maddox.

Have you got a few minutes?

Right, thanks.

That was forensics.

The bomb was made out of fulminated mercury packed into a small pipe.

You open the box, and... Boom.

Mercury's not easy stuff to get your hands on, especially not nowadays.

Okay, why don't we check if there've been any break-ins recently?

In warehouses, merchants, labs.

Oh, listen, I need to make a little detour.

I promised to buy a present for the baby.

Apparently, we're not allowed to turn up empty-handed.

No, it's bad form.

So, any ideas?

What, me?

Something that says "Oxford," metaphorically.

Pair of handcuffs?

You know Frank Guitteau's job is collecting office waste?

Picking up electrical goods, recycling, that sort of thing.

So?

There's mercury in fluorescent light bulbs.

So do you want to go back to the station, take a closer look at Frank Guitteau?

What about the present?

Nah, later.

Two years, I was on the team.

David invited me to join after I graduated.

To study knots?

It sounds mad, doesn't it?

But our research... "Our" research?

I still feel a part of it.

And yet you walked away.

Yeah, a couple of months ago.

Adam and David were heading down a dead end.

I steered them away.

And more than that, it was that study of spiral knot determinants that led to everything else.

There wouldn't have been a breakthrough if it hadn't been for me.

Afterwards, when Adam and David presented their findings, I wasn't even mentioned.

It was like they'd done all the work themselves.

I'd been photoshopped out.

I went to them, I told them I thought it was unfair, and Adam said all I'd done was the grunt work.

I hadn't made the final connection, even though it was right there in front of me.

"Grunt work."

Must have made you very angry.

I yelled a bit, yeah.

Eyewitness said you went "bat... in the atrium."

Maybe a little.

Somebody sent David and Adam Capstone threatening letters.

Not me.

Okay.

We're done.

As you can see, I still have some movement.

I've got the full Stephen Hawking to look forward to.

It's genetic, no known cure.

Is that why you agreed to fund the Capstones?

To find a cure?

I'm beyond all help.

But if their research can make a difference after I'm gone and I make it possible, that's got to be worth something, hasn't it?

A legacy.

Better than a blue plaque.

Did you know Adam Capstone?

No, not very well.

He used to come sometimes with Elizabeth, Donald's daughter, but we didn't speak much.

Were either of you aware of the allegations made by Paula Guitteau?

Well, the girl was troubled.

What she did was terrible, but that was her choice.

Adam was entirely blameless, is that what you think?

I think it's none of our business.

I suppose you're right.

I should go.

Grace'll be hungry.

LEWIS: Grace?

My three-year-old.

She's with the child-minder.

She doesn't like to be kept waiting.

Especially when food's involved, I bet.

You've got kids?

One of each.

A long time since they were three, mind.

I'll check in later.

We can do some neck stretches.

Gentlemen.

Sarah.

She lives in.

Easier to torture me.

I don't know what I'd do without her.

Wither, I suppose.

Would you excuse me for a minute?

Ms. Alderwood?

Adam Capstone.

What about him?

You didn't like him very much, did you?

Adam was a..., frankly.

Which is how he treated Elizabeth.

How did Donald feel about that?

Donald spends 90% of his day just trying to get through it.

A large part of my job is to help him do that.

Now, if that means avoiding ways of upsetting him, then fine.

So we pussyfoot around the subject, pretend that everything was okay.

Can't be easy.

I'd do anything for Donald.

MAN: No break-ins here, I'm happy to say.

Everything's kept under strict lock and key.

So who normally has access to all of the chemicals?

Students and members of staff.

We each have a key card, and everything has to be accounted for.

How hard is it to fulminate mercury?

It's not.

You just mix mercury with concentrated nitric acid and add the resulting aqueous mercury nitrate to ethanol.

Simple.

So anyone could do it?

If they have the chemicals.

Ah, Professor Dimmock, you're busy.

That's all right.

I'm being grilled by the police.

It's very exciting.

MADDOX: DS Maddox.

And you are?

Djimon Adomakoh.

DIMMOCK: Mr. Adomakoh here is one of our brightest stars, all the way from New York.

A postgraduate research fellowship beckons.

Congratulations.

I'm going to need a list of all students and staff.

Anyone who has access.

Of course.

You take security seriously here?

Students with unlimited access to chemicals and the knowledge to turn them into something illegal?

Asking for trouble, don't you think?

(panting) ELIZABETH: Mercury's a real pain.

Especially if you spill it.

So, you know, don't.

MADDOX: She's got loads of videos online.

Lectures, demos, all sorts.

She wouldn't have any problem getting ahold of mercury.

And she'd know what to do with it.

Plus she said she hates confrontation.

What, you're saying it's easier to send a bomb than just have a row?

Well, we know she resented Adam's behavior but couldn't bring herself to leave him.

Which would make her resent him even more.

And I've seen a lot of grieving widows, but never one like her.

My wife's thinking of getting a new car.

Hatchback.

Card.

DEALER: 19.

I think a bike's better.

Stand.

(phone dialing) ADAM (voicemail): Hi, it's Adam.

I'm obviously being a genius somewhere, or more likely I've forgotten my phone, so leave me a message and I promise I'll get back just as soon as I stop being a genius or find my phone, whichever comes first.

Brushing up on your chemistry?

She's good, in a Royal Institute Christmas lecture type way.

I bet you watched every one of them.

Highlight of my holidays.

Adam Capstone certainly seems to be enjoying it.

LEWIS: And so does Paula Guitteau.

I've also been checking up on Adam Capstone's emails.

I don't suppose his passcode's 060302?

Not that simple, sadly.

Never is.

Oh, hang on.

You see, these he's deleted off the computer, but they've stayed on the server.

They're emails from his brother.

LEWIS: So why delete them?

"Think of someone else for a change.

Carry on, and I'll kill you."

I'm guessing that's why.

"Carry on, and I'll kill you."

I was angry.

I said some terrible things, and I wish that, um... You argued about who would benefit from your discovery?

Yes.

Adam was all, "It belongs to the world."

And you disagreed?

Well, why shouldn't we make some money?

We've worked hard enough.

So you agreed to sell to AKGC Pharmaceutical?

Who have the wherewithal to actually develop a product that will change the world.

What we've discovered is just the first step-- the toolbox, if you like.

There's still a long way before there's a drug on the market.

And now if they want to pay us for that, where's the harm?

Adam didn't seem to think that money was the issue.

You never do when you have it.

Do you need money, Mr. Capstone?

No, as it happens.

Besides, Adam was being a bit disingenuous.

There's still money to be had.

Recognition.

Tenure at a nice, rich college in the States.

Did you like your brother, Mr. Capstone?

How can you even ask that?

Yes, we rowed.

Yes, I disagreed with some of the things he did.

But Adam knew me better than anyone, and I him.

My whole life, there hasn't been a day that he wasn't a part of.

He was my brother.

So never make the mistake, Inspector, of thinking that I didn't love him.

How well did you know Paula Guitteau?

I didn't.

I never taught her.

Adam looked after her.

You stood by your brother even after she accused him of raping her.

Yes.

And after she did what she did.

Which sort of answers your earlier question, doesn't it?

Sort of.

Look, I know the emails look bad.

It was the last thing I said to my brother and I never got the chance to put it right.

The deal still going through with AKGC?

Yes; it always was.

Now, if you'll excuse me, I have a fundraiser to attend.

Not that I really feel like it, but, you know, duty calls.

LEWIS: I realize this isn't very convenient, but I do have a couple of questions I need to ask you, if that's okay?

Did you know that David was hoping to sell their research to AKGC Pharmaceutical?

Yes.

And Adam disagreed?

It was his right.

It wasn't meant to be about getting rich quick.

So you didn't approve?

Well, the money didn't come with any strings, Inspector, but no, I didn't like it.

And now there's nothing stopping it from happening.

David had it hard growing up.

In what way?

Whatever David did, Adam did quicker.

And younger.

A Levels, Oxbridge entry.

David is brilliant, but Adam was the truly gifted one.

On the other hand, David could do all the groundwork.

Put in the hours, build the foundations.

And then Adam would come along... And steal all the glory?

Make all the difference.

And was David jealous?

He understood.

They complemented each other.

(sighs) David loved his brother, Inspector.

He'd never harm him.

Not David.

Would you like me to...?

Yes, thank you.

Came for a top-up.

Help yourself.

This not your thing?

Rubbish at all the glad-handing.

Besides, she likes my full attention when she's eating.

That's the thing about three-year-olds-- so set in their ways.

Oh, I've always wanted to go there.

I saw those when I was in Toronto.

It was winter, they were frozen solid.

Amazing.

Oh!

Try to keep hold of it, munchkin.

Always more useful that way.

When did you say that was?

What?

That you were in Canada.

Three years ago.

February, was it?

The same time that Adam Capstone was there.

How old did you say she is?

It began soon after I started here.

I was vulnerable, and Adam sensed it.

Easy pickings.

Adam was funny and attentive, and I adored him.

Or at least I thought I did.

So what happened when you found out you were pregnant?

I told him I was going to keep her.

And he made me promise not to tell anyone who the father was.

Promise in return for what?

Money?

For a while.

Then Elizabeth found out about the payments.

Adam fessed up, that was that.

So Elizabeth knew?

Where are we with the grieving dad?

Frank Guitteau?

We're still digging.

You think he could make a bomb?

Well, fulminating mercury is actually not that hard if you've got the right kit.

But even so, it's a bit specialized, isn't it?

Then there's the hate mail.

That's a major line of inquiry.

So it is.

Well, Professor Dimmock from the chemistry lab has given me a list of all those who have access to their supplies.

Start with them.

Maybe one of them has got links to the maths department we don't know about.

(phone ringing) (sighs) (phone beeps) MADDOX: This is a message for Mr. Djimon Adomakoh to call Sergeant Maddox at Oxford Police.

Thank you.

(sighs) It's not enough.

It's what we agreed.

I need more.

That's all there is.

You owe me.

I owe you what's in there.

I'm calling it a day.

What?

It's too dangerous.

We're not doing anything illegal.

Tell that to the pit boss.

Please, David.

A few more games.

Don't I deserve that?

No, we quit while we're ahead.

And you just get to decide?

That's right.

They'll find out.

You don't know that.

If the police are asking questions, they will find out.

It's going to be okay.

We'll just wait it out.

What else can we do?

Come on.

So the wife knew about the baby?

According to Sarah Alderwood, yeah.

HATHAWAY: Plus there's the money from the pharmaceutical deal her husband opposed.

With him out the way, it's sure to go through.

LEWIS: And as his widow, she stands to benefit big time.

So that's two motives and unlimited access to mercury, right?

I think I've got something.

We know that the letters sent to Adam Capstone were processed through these sorting offices: Wallingford, Thame, and Kidlington.

And this is a copy of Frank Guitteau's pick-up itinerary for the whole of the last month.

On the day the letters were sent, he had pick-ups in Thame, Kidlington... Wallingford.

FRANK: It's a coincidence, that's all.

Yes, I was in those places.

So what?

So were a lot of people.

Hey, it's my job.

Do you handle a lot of fluorescent bulbs here?

A fair amount.

Do you know how to extract mercury from them?

Of course I don't, why?

The bomb that killed Adam Capstone was made from mercury.

HATHAWAY: And you hold Adam Capstone responsible for the death of your daughter.

He was responsible.

You wanted to make him pay for what he'd done?

I wanted him to be scared.

I didn't want to kill him.

Look...

They were just letters.

Okay?

Nothing else.

He'd got off scot-free, like nothing had ever happened, whereas we... Do you know my wife spends her waking hours volunteering for every bloody charity you can think of?

She's more interested in strangers than she is me.

I couldn't save my girl, and now I can't save my wife.

I wanted to make him hurt a little.

I could do that, at least.

I'm sorry, Frank, we're going to have to take you down to the station.

Sixteen.

Card.

Too many.

Is this necessary?

Your husband didn't say anything to you about what he was doing?

No!

You had no idea?

Since Paula died, we don't say much to each other about anything.

HATHAWAY: David Capstone said he didn't know Paula.

LEWIS: He obviously gave her tutorials, too.

Look, he marked some of her papers.

Yes, Mr. Capstone, it's DI Hathaway.

I need to ask you a few more questions, clarify a few things.

Yes, see you in half an hour.

David.

We've been through this.

After everything I've done for you.

Go home, Andrew.

What did you get, in the end?

Sorry?

For the baby.

Nothing yet.

I haven't found the right thing.

Go on.

You should probably tell Laura, you know.

What?

That you don't want to go.

Look, I just haven't got around to buying anything, that's all.

Right.

I forgot.

And that's not symbolic.

(doorbell rings) (loud opera music playing inside) Mr. Capstone?

(doorbell ringing) (knocking) David Capstone?

DAVID: Help me!

LEWIS: David?

In here!

Shut that row off, will you?

(music stops) What do I do?

Just put it down very carefully.

Give me bomb disposal, 119 Oldfield Road.

I can't, it'll go off.

Nice and gentle.

David, look at me.

Just put it down very slowly.

You can do this.

I don't want to die.

Nobody's going to die.

(explosion) Sir?

It's Lewis and Hathaway.

There's been another explosion.

(crying) (sirens blaring) Mommy!

Mommy!

Your daughter needs you.

Are you okay?

Getting there.

At least he's alive.

How are you doing?

Superficial bruising.

Yeah, me too.

How's your hearing?

Mine's rubbish.

It's like being underwater.

What?

I said how's...

Very funny.

HATHAWAY: Have you called Laura?

She's not picking up.

I left her a message.

Oh, God.

What were you thinking?

Well, we didn't exactly have a plan, sir.

You should've retreated to a safe distance and let the bomb squad take over.

And to hell with David Capstone?

I don't like my men being blown up.

I'm not a huge fan of it, myself.

It's because he cares.

So what did they say about Capstone?

He'll live.

He's lucky.

I think you all were.

(sighs) Ow!

Well, I think I've leave you guys to get on with it.

What was that for?

For putting yourself in harm's way.

And that one's for the message you left.

What was wrong with it?

"I'm okay, it was only a small bomb"?

Well, it was only a small bomb.

Idiot!

Hey.

Listen.

I'm not going to go to New Zealand.

But we're all set.

Yeah, I probably should've said something sooner, but...

I know it's a long way and it's my family and not yours... That's not it.

And the place'll be full of baby stuff...

I'm scared, Laura.

If I go now, I'm not sure there'll be anything for me when I come back.

Of course there will.

Moody's not going to sack you when you're out of the country.

That's exactly what he might do.

Anyway, he doesn't have to sack me.

I'm a consultant.

All he has to do is not renew my contract, which will be very easy if I've been away for a while and people have forgotten I exist.

Well, what am I meant to do, go on my own?

We planned this together, Robbie.

It's the trip of a lifetime.

And it will be.

This is ridiculous.

You're being ridiculous.

What if I'm not?

No one's going to forget you, Robbie.

I've seen it happen.

Would it be the end of the world if it did?

This is what I know.

This is who I am.

I tried being away, and I'm rubbish at it.

This is what I do, and it's what I want to do till the day they carry me out of here.

Like Morse?

Well, there are worse ways.

I'm sorry, love.

I know you are.

Sorry to disturb.

Go.

Be brilliant.

Sorry, Lizzie, what were you saying?

Good news.

We got lucky.

Part of the package that the bomb came in survived the blast.

We know where it was posted.

MADDOX: 11:43 yesterday morning.

LEWIS: Is this the best we can do?

Afraid so.

Well, we've got a time and a place, at least.

Let's see where everybody was.

Yeah, starting with Frank Guitteau, our letter writer.

How could I send it?

I was at work.

Not at 11:43, you weren't.

According to your boss, you were out alone all morning.

I had a pick-up.

Office furniture out near Marston.

You can check.

We did.

They confirmed you left at 10:15.

You weren't seen back at the depot until after midday.

LEWIS: Which gives you plenty of time to have posted that parcel.

Did David Capstone know Paula well?

I don't know.

I mean, she probably attended his lectures, but she didn't go to any of his tutorial groups or anything.

And when she accused Adam of rape?

He stuck by his brother, of course.

Like everybody else.

Just when Paula needed some friends... And you resented him for that, did you?

So I wanted to blow him up, is that right?

Did you?

(laughs) Of course not.

When can I go home?

Kate?

I've got a few questions for you.

Well, can't it wait?

No, not really.

Inside?

(sighs): Okay.

Well, how can I help you?

I wondered if you would mind telling me where you were yesterday morning?

What, are you asking me for an alibi or something?

Okay.

I was in a lecture until 10:30, and then I worked on a problem with the 3D printer.

Mr. Adomakoh.

I've left you a message.

Yes, I was busy.

Sorry.

I was just leaving anyway.

I saw you earlier, didn't I?

Outside David Capstone's house.

Yes, I was running.

My route took me past his house.

I was interested.

Where were you yesterday?

Why are you asking him that?

Lectures.

All morning?

Professor Mowbray likes to take his time.

And did anybody see you?

I don't know, you'll have to ask.

Yeah, I will.

Thank you.

And if I've got any more questions, then I know where to find you now, don't I?

Why try to kill both brothers?

Well, the first bomb was pretty clumsy.

There was no guarantee that he'd get Adam.

It could have just as easily blown up his secretary.

There was no danger of that with this morning's effort.

I just phoned Elizabeth Capstone.

She said Adam often didn't even go in to work until gone 11:00.

Left all the admin to David.

What, so you're saying that Adam was a mistake and that David was the intended target?

Well, two bombs in three days, someone wants whoever dead in a hurry.

What?

Come on.

David Capstone's just about to cash in on years of research.

Apart from his brother, who else would hate to see that happen?

The person who saw it as their legacy.

Oh, you're wasting your time.

And mine.

We think Adam was killed by accident and that David was the bomber's intended target.

What's that got to do with me?

LEWIS: Well, you'd invested all that money for the greater good, and there's David selling to the highest bidder.

HATHAWAY: Just when you thought you were going to leave something worthwhile behind.

Did you try and stop him?

Oh, sure.

I threw together a parcel bomb because dexterity is one of my strongest points.

I wrapped it up, put on a stamp, went into town, and posted it.

You could've had help.

Where were you yesterday morning?

Oh, leave her out of it.

(coughing) It's okay.

I was out yesterday morning, running errands.

What sort of errands?

That's enough!

I want you to go now!

In a moment.

Ms. Alderwood?

To the bank and then the shops.

Will you leave?!

Out!

(coughing) What was it you said?

You'd do anything for him?

Can you think of anybody that would want to hurt you, Mr. Capstone?

Well, I'm assuming it was whoever sent those threatening letters.

Well, we believe those were directed at your brother.

Then no, sorry.

What about Kate McMurdoch?

Well, it's possible, I suppose.

I mean, I was the one who brought her in.

I was her mentor.

I was the one who had to explain to her the realities.

Plus she has a sense of entitlement a mile wide.

Sorry.

It's been a long day.

Can we give you a lift home?

Or is there somewhere else you'd rather go?

No, no.

I just want to go home.

I would invite you in, but... We need to be getting back.

Well, there is just one other thing.

You said you didn't know Paula Guitteau, and yet you marked some of her papers.

Well, I marked one of her papers when Adam was away, but I didn't know her.

That was at a Christmas party.

I think the whole faculty were there.

I don't remember that, but then I was probably in about a hundred selfies that evening.

Sorry.

Do the numbers "060302" mean anything to you?

Are they important?

We found them at Paula Guitteau's home.

Combination or something?

Well, if you think of anything... Yeah, of course.

Uh, Inspector?

You wait here.

(groaning and grunting) He promised me money.

And then he went back on his word.

I knew where he kept it, and I thought the house would be empty after what happened.

Why did you need money?

I have debts.

HATHAWAY: What sort of debts?

Gambling.

I developed a taste.

It's so easy, you have no idea.

And David Capstone said he'd pay them off?

That's right.

We're a team.

Although the other players think that we're strangers.

We play the casinos.

London, Birmingham, Manchester once.

And most of the time, we win.

I thought the casinos did most of the winning.

Not if you cheat.

That's the lot.

Are you okay?

I'm fine.

There is one thing.

The drawer.

Donald... For everything you've done.

I don't know what to say.

Don't say anything.

Just think about it.

A little security.

For Grace, obviously.

I couldn't care less about you.

David would watch the cards being dealt, memorizing who got what, calculating the odds of getting a particular card next, and then he'd tell me.

How?

Code.

He seems to be talking gibberish: his wife, how he's going to buy a car.

From what he can see, David calculates the optimal play for any situation, and then he adjusts it so it's not to look suspicious.

He's got over a thousand plays in his head.

And afterwards, you divide the winnings.

70-30.

Except you wanted more.

Well, why not?

He made enough out of me.

Well, being refused, desperate, I can understand you'd resent him.

And you know how to fulminate mercury.

Except I didn't.

That wasn't me.

Where were you around 11:40 yesterday morning?

I was lecturing second years, about 40 of them.

The lecture ended at midday.

And what about the day before Adam Capstone was killed?

Where were you then?

I was...

I was lecturing in the morning, I had a tutorial group in the afternoon, and then I was playing blackjack in the evening.

LEWIS: Alone?

With David.

LEWIS: How well do you know him?

I don't, not really.

I met him at a college dinner.

I thought he might be useful when I was looking for a partner.

Doesn't look like a pro, you see?

He blames you for his gambling debts.

I led him to water, but I didn't make him drink.

But then it's never the fault of the addict, is it?

What's going to happen to him?

Do you want to press charges?

No, he's got enough problems as it is.

I don't want to add to that.

(doorbell rings) Excuse me.

Mrs. Capstone.

Elizabeth was just checking up on me.

I was worried.

They're my Borromean rings.

I had them printed on the 3D printer the other day.

Three interlocked rings, but no two of them are linked.

If any is cut, it disintegrates.

Intriguing, isn't it?

My favorite knot.

I read somewhere that they're a symbol of love.

Two rings, separate, held together by something... other.

Without it, everything falls apart.

ELIZABETH: That's a bit sentimental, isn't it?

Who came up with that?

I'd say the recipient of an Arts degree.

What did you make of Elizabeth Capstone showing up like that?

Natural concern for her brother-in-law?

No, I didn't think so either.

As Adam Capstone's widow, she stands to benefit from the deal with the drug company going through, right?

What, so she bumps off her husband who gets in the way of the deal who, incidentally, is also cheating on her?

Sort of two-for-one.

Yeah, but then why kill him before the deal's gone through?

That doesn't make much sense.

We just need to work out the twist and writhe, that's all.

Twist and writhe?

The particular set of moves that'll unpick a given knot.

I'm getting bloody sick of that thing.

(phone ringing) Hello?

Okay.

Um, thank you.

That was the care home.

Dad's taken a fall.

(door opens) I got him a newspaper.

And some magazine about trout fishing.

You just missed the doctor.

I thought he just bruised his hip?

Hey Dad, it's me.

I've brought you a few things I thought you might like.

You should stop wasting your time selling dusters and rubber gloves.

Get yourself a proper job.

They say he's had a series of mini-strokes.

Now piss off.

I want to watch the cricket.

Are forensics back from the scene?

Yeah, they found mercury from the blast.

Also sulphur, lime, and magnesium.

MADDOX: Almost certainly from the detonator.

That's a lot of chemicals.

Which could've easily been accessed by Kate McMurdoch's boyfriend.

Djimon Adomakoh.

Chemistry student.

LEWIS: Claims that he was at a lecture when the second bomb was posted.

Only he wasn't?

I can't find anyone to vouch for him, at least not yet.

What do we know about him?

Foreign student.

He lives in New York.

Family are originally from Ghana.

He is the star of the year.

He's already been offered a post-grad research fellowship.

We think he and Kate McMurdoch might be working as a team.

She blames David for stealing her research, kills Adam by mistake.

But she already knew David's home address.

If she was going to kill him, why would she send the first bomb to the maths department?

I've got the Guitteau phone records here that you asked for.

All these are landlines to Deermarsh prison.

Why?

Apparently, Joyce Guitteau has been visiting a right-to-lifer there.

Gordon Jensin.

I remember him.

Yeah.

The last time was four days before Adam Capstone died.

What's this Jensin bloke in for?

He sends bombs.

Yes, I went to see Gordon.

I'm a prison visitor.

It's one of the charities that I support.

She sees a lot of prisoners, so what?

They don't all know how to make bombs.

Gordon Jensin hasn't got any friends or family.

He's not a hardened criminal.

He's alone and scared, and I visit him because no one else will.

Do you honestly think we spend our hour discussing how to make bombs?

Can I ask you where you were around 11:40 the day before yesterday?

Why?

We know what time the second bomb was posted.

You couldn't pin it on me, so now you're having a go with her?

Is that how it works, Inspector?

Please just answer the question.

First, you lot fail my daughter when she really needed you, and then you go and let a guilty man free and then stand by while we pay the price.

You're angry, I understand.

All you've got is supposition and coincidence.

Now, you tell me what gives you the right... You have motive.

You sent those letters.

You had access to mercury.

Your wife knows a convicted bomb maker!

I'm sorry.

But there's a man dead.

There's another man nearly died.

So yes, I have the right.

I was at the hospice.

You can check.

They'll vouch for me.

Thank you.

So I've checked, and the lecture that day only lasted for an hour.

Not the whole morning, like you said.

Where were you?

I went to go and get something to eat.

From where?

There's cafes round the corner.

Is this your family up here?

Yes.

They must be very proud.

I hope so.

How long have you and Kate been together?

Two-and-a-half years.

That's very impressive.

Most student relationships only last two-and-a-half months.

Yeah, but not in this case.

(yawns) He's asleep.

Maybe you should get some, too.

I'm all right.

Liar.

Will you stop by later?

Well, there isn't any point, is there?

I think there is.

He doesn't know who I am.

I wasn't talking about Dad.

He is running out of teeth to lie through.

First of all, it was the lecture.

Then it was the cafe.

And he wasn't there either?

Well, for all of about ten minutes, according to the owner, but not for the hour and a half that he claims.

So what's he hiding?

He's besotted with Kate McMurdoch.

He'd do anything for her.

What, like make a bomb?

In a heartbeat, I reckon.

If she asked him.

Don't forget, these two work in the same department.

So does she.

Maybe we're looking at this all wrong.

Maybe it's nothing to do with Djimon and Kate.

No, there's something else that bothers me.

In his room, he's got pictures of his family all over the wall: his mom, dad, brothers, sisters... Well, he's a long way from home.

Yeah, exactly, so you'd think that at least one of them would feature New York, but not one of them does.

So I've checked his phone records.

He has not sent a text or made a call to the U.S. in the whole time he's been here.

Not one.

♪ ♪ ♪ ♪ (door opens) Sorry, sorry.

I had to go out.

Spur of the moment thing.

Here, let me help.

I thought you were sleeping.

I was.

HOBSON: Massive blast trauma to the head, I'm afraid.

It blew up in his face.

It blew up while he was making it?

Well, I'll know more after the post mortem, but I'd say so, yes.

Why wasn't I called?

I thought you were with your dad.

Well, I should be here, shouldn't I?

You should be there.

We can cover this.

Go, hold his hand.

We don't do holding hands.

HOBSON: At least I'm leaving you with an interesting one.

Something to keep you busy while I'm gone.

Why?

What've you found?

Andrew Dimmock wasn't blown up.

At least, that's not how he died.

When you're killed in an explosion, you get severe pulmonary contusion, bleeding and swelling around the lung-- blast lung, we call it.

And if the bomb doesn't kill you outright, the blast lung will finish off the job.

HATHAWAY: And he doesn't have that?

Plenty of external damage, some penetrating trauma, but no injuries associated with inhalation of any kind.

But his hyoid bone was fractured.

There may be some bruising which hasn't developed yet, but even so, I'd say Andrew Dimmock was strangled.

I've booked a taxi for tomorrow.

It's picking me up at 9:00.

Well, I can take you.

You've got work to do.

And I'm not very good at airport goodbyes.

Well, there must be something I can do.

You can sit on my suitcase, help me close it.

I'll see you later.

So you've decided not to go?

That's right.

That is your decision?

Come on, then, spit it out.

I was just wondering why you changed your mind.

You know, you were keen.

I'm wondering what's happened.

Nothing's happened.

Well, if it isn't something that's already happened, then it's something that you think will happen.

Have you quite finished?

Oh, you're worried if you go that Moody'll close you down.

Oh, rubbish, man.

Yeah, you'll come back and you won't be a copper anymore.

And if you're not a copper, then what will you be?

Shouldn't I be lying on a couch for this sort of guff?

Do you love Laura?

Then go.

Show her that you love her.

Don't assume that she knows.

People make that assumption and it's a mistake.

Still.

Your decision.

I've checked Djimon Adomakoh's immigration status.

Don't tell me-- illegal?

No, no, his visa's fine.

But according to Border Control, Djimon Adomakoh isn't even in the country.

He flew back to the States nine months ago.

Bring him in.

Okay.

I'm sorry if I overstepped the mark.

You're overreacting.

I won't let them destroy us!

They can't.

I told you, we just wait... We are past that now!

We have been for a while.

Whoever it was, they almost certainly knew Andrew Dimmock.

Because?

No sign of a break-in at the lab.

So either he let them in, or...

They had their own key.

Why him?

Sorry?

All these suspects.

Why pick Dimmock to frame?

Because it creates a narrative that we'll follow and he comes with a ready-made motive.

So which of them knew that?

Well, Elizabeth Capstone worked in the same lab as him.

LEWIS: He knew Donald Lockston socially and, by extension, Sarah Alderwood.

HATHAWAY: Kate McMurdoch didn't know him and Djimon Adomakoh did.

LEWIS: Sergeant Maddox is picking him up now.

You see, all along, the killer's been hidden.

Everything's happened at arm's length.

But yesterday, for the first time, they had to be at the scene to frame Dimmock.

They had to show themselves.

Where are you going?

I'm going back.

This time, the killer's been forced out of their comfort zone, so maybe this time, they've made a mistake.

I'll come with you.

No, I'm fine on my own.

Tell me about Djimon Adomakoh.

My name is Joseph Donadu.

I live in Ghana.

After school, I used work in the evenings so I could sit my A Levels.

And when I got the grades I needed, when it meant I could come here and apply... someone in the Foreign Office, or the Home Office, decided that they didn't want a kid from Ghana studying chemistry.

Something about all that knowledge being used dangerously, I suppose.

So my visa application was refused.

Too bad, eh?

But I'd worked too hard to just...

So you impersonated someone else?

My cousin Djimon.

He lives in America.

There's no restrictions, you see.

He applied instead?

And he came for the interview.

It worked brilliantly.

Until you got offered the post-grad research position.

I needed Djimon to come back so I could extend my visa.

That's why I lied about where I was.

They will send me back home, won't they?

Yeah.

Yeah, I expect so.

You know, all I wanted to do was learn.

That's all I wanted to do.

But instead, I met...

I thought not getting a degree was the worst thing that could happen.

I was wrong.

(door opens) Fresh pair of eyes?

Djimon Adomakoh is not the bomber.

He's not even Djimon Adomakoh.

Fake ID for a student visa.

Anything?

I don't know, maybe.

These are the forensic reports for the three bomb blasts, and at David Capstone's, there were traces of calcium hydroxide and sulphur, but not the other two.

Why do you think that is?

Maybe the bomber used a different detonator.

Right, I'd better get Djimon's arrest report written up.

Calcium hydroxide's another name for lime.

Sulphur and lime.

MOODY: You think that's true?

"Work alone is noble"?

Bit outdated, isn't it?

Being noble?

I'm not sure I even know what it means anymore.

Yeah, you do.

There's nothing here.

Probably not.

Sir?

(sighs) ELIZABETH: Along with the usual paraphernalia, it's useful to have a mercury spillage kit which contains sulphur and lime, which reacts with the mercury and stops it rolling about.

(phone rings) Yeah?

LEWIS: James?

060302.

I know what it means.

I know who sent that card to Paula.

Me too.

I told the cab to wait.

What do you think?

Very distinguished.

Going for understated elegance with a hint of boffin.

Bull's-eye.

(doorbell ringing) Oh, I told him we'd be a few minutes.

Mr. Capstone.

Can this wait?

We're announcing the deal with AKGC Pharma this evening.

No, sir, I'd like to do it now.

If you'd excuse us?

I've got nothing to hide.

Were you in love with Paula Guitteau?

Don't be absurd.

"Always remember, 060302."

That's what you wrote to her, isn't it?

I'm sorry?

Six-three-two.

The link symbol for the Borromean rings.

Your favorite knot.

Also your little in-joke with Paula.

I told you, I barely knew her.

Two rings, unconnected, held together with a third?

Without it, everything else falls apart.

LEWIS: You were in love with her.

I think I'd like you to leave.

Just like her parents, you held your brother responsible for her death, and you all wanted revenge.

The difference was, they sent him angry letters.

You send him a bomb.

And your proof?

The rings are well-known.

Anyone could've sent that card.

Who said anything about a card?

Adam wasn't the intended victim, I was.

Andrew Dimmock killed the wrong person and tried to put it right-- that's what happened.

HATHAWAY: No, that's what you wanted us to believe.

After all, how could you be the murderer if you were also the intended victim?

LEWIS: I'm sure you intended to set off the second bomb here once you were at a safe distance.

Then you heard we wanted to talk to you, so you waited until we arrived and used us as witnesses.

HATHAWAY: You promised to pay off Andrew Dimmock's gambling debts if he procured the mercury for you, and then later, the sulphur and the lime needed to clean up after one of your spillages.

LEWIS: The more desperate he became, the more of a danger he posed.

He was a loose cannon.

You had to shut him down.

HATHAWAY: So you gave us the murderer, killed by his own bomb.

Except he wasn't, was he?

You strangled him and then tried to frame him.

David?

Tell me they're wrong.

Adam always said you used to bear grudges.

Even as a kid.

Store it up, let it fester.

That's nonsense.

What's the matter?

Didn't like baby brother being cleverer?

No.

Better looking, more successful?

What, you think I was jealous?

Then why?

Because of Paula!

I...

I thought, "Finally.

"Someone I could share a life with.

Something good that was mine."

But Adam couldn't...

He had to spoil that, too.

He told her about the gambling, made it seem grubby, like I had a problem.

I tried to speak to Paula after that, but she wouldn't listen to me.

She was so ashamed.

And then she...

He broke the only thing that mattered to me because he could.

My brother.

What am I going to do without him?

♪ ♪ It'll be here when you get back.

That's what I'm afraid of.

I've got something for you.

What do you think?

Thank you.

It's perfect.

The dodo?

Famous Oxford icon.

And a bird that I can relate to.

Except you're not extinct.

Well, let's hope that's still the case when I get back.

From New Zealand.

Where I will have been.

With you.

If that's okay.

I think I've been a bit of a fool.

Well, actually, I've been a lot of a fool.

I'm really sorry.

I'll make it up to you, I promise.

And I won't forget.

Yeah, you will.

But I'll remind you.

(laughs) Robbie.

Demob happy?

Something like that, sir.

You know, I would never have caught that knot clue.

You did.

Sir.

Have a safe trip.

See the sights, recharge your batteries.

I need you match-fit if you ever want to come back.

Thank you, Joe.

I came to say goodbye.

Oh.

It's not going to be the same without you.

Nah.

Do you fancy a drink?

Oh, I can't.

I've got a girls night.

We're celebrating.

Tony's decided to take the job for another year, so... Well, is James around?

I'll say cheerio.

No, he's gone for the night.

Ah.

Well, not to worry.

Give him a call.

Nah.

It's not important.

Well, don't forget about us.

HATHAWAY: "For Christ plays in 10,000 places.

"Lovely in limbs, and lovely in eyes not his.

To the Father through the features of men's faces."

The taxi should've been here by now.

I thought they were reliable.

They are.

(laughs) ♪ ♪ I'm going to get something to read.

For talking him round.

Long flight.

Nearly 24 hours.

Worth it, though.

Have to get there first.

You'll be missed.

Better be.

Have fun-- you deserve it.

So do you.

You have to get there first.

Okay?

♪ ♪ Go to the Masterpiece website.

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To order this program on Blu-ray or DVD, visit shopPBS.org or call us at 1-800-PLAY-PBS.

Captioned by Media Access Group at WGBH access.wgbh.org