“You really think he could have killed his father then driven coolly down to Woolstone to wait with Kinvara until the police arrived?”

“Forget psychology or probability: we’re considering opportunity,” said Strike, blowing out a long jet of smoke. “Nothing I’ve heard so far precludes Raphael being at Ebury Street at six in the morning. I know what you’re going to say,” he forestalled her, “but it wouldn’t be the first time a phone call had been faked by a killer. He could have called his own mobile with Chiswell’s to make it seem as though his father had ordered him down to Woolstone.”

“Which means that either Chiswell didn’t have a passcode on his mobile, or that Raphael knew it.”

“Good point. That needs checking.”

Clicking out the nib of his pen, Strike made a note on his pad. As he did it, he wondered whether Robin’s husband, who had previously deleted her call history without her knowledge, knew her current passcode. These small matters of trust were often powerful indicators of the strength of a relationship.

“There’s another logistical problem if Raphael was the killer,” Robin said. “He didn’t have a key, and if his father let him in, it would mean Chiswell was awake and conscious while Raphael pounded up anti-depressants in the kitchen.”

“Another good point,” said Strike, “but the pounding up of the pills has to be explained away with all of our suspects.

“Take Flick. If she was posing as the cleaner, she probably knew the house in Ebury Street better than most of the family. Loads of opportunities to poke around, and she had a restricted key for a while. They’re hard to get copied, but let’s say she managed it, so she could still let herself in and out of the house whenever she fancied.

“She creeps in in the early hours to doctor the orange juice, but crushing pills in a pestle and mortar is a noisy job—”

“—unless,” said Robin, “she brought the pills already crushed up, in a bag or something, and dusted them around the pestle and mortar to make it look as though Chiswell had done it.”

“OK, but we still need to explain why there were no traces of amitriptyline in the empty orange juice carton in the bin. Raphael could plausibly have handed his father a glass of juice—”

“—except that Chiswell’s prints were the only ones on there—”

“—but would Chiswell not find it odd to come downstairs in the morning to a pre-poured glass of juice? Would you drink a glass of something you hadn’t poured, and which appeared mysteriously in what you thought was an empty house?”

Down in Denmark Street, a group of young women’s voices rose over the constant swish and rumble of traffic, singing Rihanna’s “Where Have You Been?”

“Where have you been? All my life, all my life…”

“Maybe it was suicide,” said Robin.

“That attitude won’t get the bills paid,” said Strike, tapping his cigarette ash onto his plate. “Come on, people who had the means to get into Ebury Street that day: Raphael, Flick—”

“—and Jimmy,” said Robin. “Everything that applies to Flick applies to him, because she would’ve been able to give him all the information she had about Chiswell’s habits and his house, and given him her copied key.”

“Correct. So those are three people we know could have got in that morning,” said Strike, “but this took much more than simply being able to get in through the door. The killer also had to know which anti-depressants Kinvara was taking, and arrange for the helium canister and rubber tubing to be there, which suggests close contact with the Chiswells, access to the house to get the stuff inside, or insider knowledge of the fact that the helium and tubing were already in there.”

“As far as we know, Raphael hadn’t been in Ebury Street lately and wasn’t on terms with Kinvara to know what pills she was taking, though I suppose his father might have mentioned it to him,” said Robin. “Judged on opportunity alone, the Winns and Aamir seem to be ruled out… so, assuming she was the cleaner, Jimmy and Flick go to the top of our suspect list.”

Strike heaved a sigh and closed his eyes.

“Bollocks to it,” he muttered, as he passed a hand across his face, “I keep circling back to motive.”

Opening his eyes again, he stubbed out his cigarette on his dinner plate and immediately lit another one.

“I’m not surprised MI5 are interested, because there’s no obvious gain here. Oliver was right—blackmailers don’t generally kill their victims, it’s the other way around. Hatred’s a picturesque idea, but a hot-blooded hate killing is a hammer or a lamp to the head, not a meticulously planned fake suicide. If it was murder, it was more like a clinical execution, planned in every detail. Why? What did the killer get out of it? Which also makes me wonder, why then? Why did Chiswell die then?

“It was surely in Jimmy and Flick’s best interests for Chiswell to stay alive until they could produce evidence that forced him to come across with the money they wanted. Same with Raphael: he’d been written out of the will, but his relationship with his father was showing some signs of improvement. It was in his interest for his father to stay alive.

“But Chiswell had covertly threatened Aamir with exposure of something unspecified, but probably sexual, given the Catullus quotation, and he’d recently come into possession of information about the Winns’ dodgy charity. We shouldn’t forget that Geraint Winn wasn’t really a blackmailer: he didn’t want money, he wanted Chiswell’s resignation and disgrace. Is it beyond the realms of possibility that Winn or Mallik took a different kind of revenge when they realized the first plan had failed?”

Strike dragged heavily on his cigarette and said:

“We’re missing something, Robin. The thing that ties all this together.”

“Maybe it doesn’t tie together,” said Robin. “That’s life, isn’t it? We’ve got a group of people who all had their own personal tribulations and secrets. Some of them had reason not to like Chiswell, to resent him, but that doesn’t mean it all joins up neatly. Some of it must be irrelevant.”

“There’s still something we don’t know.”

“There’s a lot we don’t—”

“No, something big, something… fundamental. I can smell it. It keeps almost showing itself. Why did Chiswell say he might have more work for us after he’d scuppered Winn and Knight?”

“I don’t know,” said Robin.

“‘One by one, they trip themselves up,’” Strike quoted. “Who’d tripped themselves up?”

“Geraint Winn. I’d just told him about the missing money from the charity.”

“Chiswell had been on the phone, trying to find a money clip, you said. A money clip that belonged to Freddie.”

“That’s right,” said Robin.

“Freddie,” repeated Strike, scratching his chin.

And for a moment he was back in the communal TV room of a German military hospital, with the television muted in the corner and copies of the Army Times lying on a low table. The young lieutenant who had witnessed Freddie Chiswell’s death had been sitting there alone when Strike found him, wheelchair-bound, a Taliban bullet still lodged in his spine.