"Like you were, with the cancer idea? Im supposed to believe my disapproval could provoke new cancer in my sister?"

She watched Simons controlled exhalation with satisfaction. His turn to practice counting to ten. And when he got there, he would find himself still married to Charlie. "Theres no cat in the HR office," he said. "And I know Im not allergic to cats. You cant claim that a known falsehood-"

"Ive just proved that its possible, in some circ.u.mstances, to know what your motivation isnt without knowing what it is. I rest my case. Put these away." She handed Simon two clean pasta bowls, steaming from the dishwasher. "There are some reasons we have that we know about, some we have that we dont know about, and some we dont have, which, when we hear them, we recognize as reasons we would never have because theyre not the sort of thing that would ever cross our minds."

"Lets say youve killed someone, all right?"

"Can you put those bowls away before you get distracted and drop them?"

"You admit it."

"I admit it," said Charlie. "It was me."

"I ask you why. You say you cant tell me-there is no reason. You dont know why. You just did it."

"Did I plan to do it?"

"You say not. It was spur-of-the-moment. Imagine I suggest to you a reason why you might have done it, and its a reason that, if you confirm it, might get you a lighter sentence or even keep you out of prison if youre lucky."

Charlie raised her eyebrows. "What, you mean that perfectly acceptable motive for committing murder that judges and juries are so lenient about?"

"A motive thatd make it not murder, but a less serious crime. Maybe."

"But . . . it wasnt my real motive?"

Simon considered her question. "Either it was, and youre pretending it wasnt, or it wasnt and youre not willing to pretend it was to avoid jail time. In either case, why?"

Charlie smiled. "Or . . ." she said. Simon stared at her expectantly. "Youre not going to like it," she warned him. "Its as devious as it is unlikely."

"Tell me. You know how I feel about Occams razor. The simplest answer isnt usually the right one. Devious and unlikely is everywhere."

"You ought to launch your own theory: Occams beard, you could call it. Okay, lets say your killer could halve the time he spends behind bars by confessing his true motive, the one you suggested to him. If hes desperate or a pessimist he might go for that. But if hes confident and a good liar, he might deny his real motive and insist as unconvincingly as he can that the crime he committed was full-on murder. Part of that implausibility might include pretending he has no idea why he did it."

Simon was nodding. "If he keeps saying he doesnt know why, and I suspect him of lying, I start to think hes not the killer, hes covering for someone. Exactly what Ive been thinking. If I find someone else to pin it on, then he doesnt go to jail at all: he gets to be innocent of the greater crime rather than guilty of the lesser one."

"Simon, its so unlikely-that itd occur to him, that hed have the nerve to carry it through. Hed have to know there was someone else who could have done it, someone with motive and opportunity. Even then, hed a.s.sume you wouldnt be able to prove it, wouldnt he? Any proof there is will point to him, the real killer."

The doorbell rang, then rang again straightaway, more insistently. "Granted, its a top idea," Charlie called over her shoulder as she went to answer it. "Sadly, its my idea, not your suspects."

"Dont let her in!" Simon bellowed.

"Shout a bit louder and you might drive her away before I get there."

More ringing of the bell. Charlie swore under her breath as she opened the door. "Sorry, youve missed your slot. Youll have to make another . . ." Appointment. The last word didnt make it.

The woman standing on the doorstep in the driving horizontal rain wasnt Liv. Charlie didnt know who she was, though there was something familiar about her. Yet this was a face she had never seen before, Charlie would have sworn to it.

"Are you Sergeant Charlie Zailer?"

"Yes. Who are you?"

"My names Regan Murray."

Dont know the name, dont know the face. And yet . . .

"Im looking for DC Simon Waterhouse. I know he lives here."

As if Charlie was about to deny it. "Simon," she called, without taking her eyes off their visitor. "Regan Murrays here to see you." At least she didnt need to worry about what she normally worried about. Regan Murray wasnt attractive; no one could think she was. She had a severe face, especially for a woman. Her eyes were too small, her forehead too dome-like.

She was bound to be something to do with the Dont Know Why Killer. Charlie realized shed been a.s.suming this hypothetical person was a man. Could Regan Murray be the Dont Know Why Killer? If she hadnt yet been arrested or charged . . .

"Who?" said Simon.

Not wreckage washed up on the doorstep by the latest case, then. Come to think of it, how did Ms. Murray know Charlies name too, and that she and Simon lived together? There was also the coincidence of the timing: Liv, whod said she was coming, hadnt turned up, and this stranger had. "Has my sister sent you?" Charlie asked. Was that why she looked familiar? One of Livs old school friends?

Simon appeared by her side. "I dont know any Regan Murrays," he said to the one in front of him.

"This is a little bit awkward. Can I come in?"

"Not unless you give us a good reason," Charlie told her.

"Not unless anything," said Simon. "I dont know you."

Listen to us, Charlie thought. Host and hostess of the year. This was what happened when you dealt with dangerous, untrustworthy people every day of your working life.

"You do know me," Regan Murray protested, pushing the door open as Simon tried to close it. "Or, rather, youd know my name-what my name used to be. Murrays my husbands name, which I took when we got married, and Regan . . . it wasnt the name I was born with. If youll let me in, Ill explain."

"It might have to work the other way round," said Charlie. "Youve got about ten seconds."

The woman shielded her eyes from the rain with her hand, so that she could get a better look at Simon as she spoke to him. "Fair enough," she said. "Im Amanda Proust. Your boss daughter."

3.

THURSDAY, 10 MARCH 2011.

"Lisa? Its me. Youre not going to f.u.c.king believe this. Guess where I am now? On another f.u.c.king coach. Yeah. Yeah, thats right. All of us, on coaches taking us away from Cologne Airport, when weve just spent two f.u.c.king hours getting there. Theyve said the crew thats supposed to be flying us home have gone past their limit, or something. What? Dunno.

"Everyones saying were off to a hotel, but no one really knows anything. No, I dunno. Ill ask Gaby. Lisa says, is there anyone on here from the airline who might know whats going on?"

"No one," I say. "Just us and the driver. Who speaks no English." No point in shielding Lisa from the awful truth. When we boarded this coach for the first time, outside Dsseldorf Airport, I a.s.sumed Bodo Neudorf would be coming with us. He seemed to be very much one of the gang at that point: helping elderly pa.s.sengers and children up the steps, leaning in and counting us all every so often, as if the trip to Cologne Airport was his own personal project. I a.s.sumed he would wish to oversee it from start to finish, but apparently not. When the door finally slid shut he was on the wrong side of it, having delegated the job of being our rea.s.suring Fly4You liaison guy to n.o.body.

I turned and watched his lean, straight-backed figure shrink into the distance as we drove away, and was struck by the deceptiveness of appearances. It looked as if we had abandoned him, but he would be fine; we, on the other hand, were alone, all two hundred of us-alone in a hollow, uncontoured way that felt endless, a way that someone like Sean wouldnt be able to imagine and has certainly never experienced. No one has, unless theyre a regular air traveler. Or perhaps severely depressed, or terminally ill and on the brink of death. There is nothing more isolating than hurtling through a stormy German night with a random collection of anxious strangers, all chasing the rumor of a plane.

"Lisa says, how can the crew have gone past their flying limit when theyve been sitting on their a.r.s.es necking cups of tea and waiting for us all night? She says its not like theyve been flying anyone else around to kill time, is it? Someones f.u.c.king been lying to us!"

Lisa: thirty-three-year-old nail technician with two toddlers from a previous relationship, now married to Wayne Cuffley and stepmother to twenty-three-year-old Lauren Cookson, who looks much younger than she is, and whom I am currently sitting next to. Im on her "JASON" side, not her "FATHER" side. The "JASON" tattoo is even bigger, with red hearts on green stalks inside the holes of the "A" and the "O." Jason is Laurens caretaker-c.u.m-gardener-c.u.m-handyman husband. He has done the Ironman challenge three times.

It would be hard to overstate how much I have learned about Lauren and her family in the past two hours-more than I would have thought possible. All she knows about me is the one detail I have volunteered: that my name is Gaby.

"The time they spend hanging around Cologne Airport waiting for us counts as time on duty," I tell her. "Do you really want someone whos been awake too long to fly you home?"

"I dont care who flies me home, long as someone does," Lauren says shakily into her phone. "Lisa, I swear, Im going crazy here. Im panicking. I need to get home. What? Yeah, course I will." She clutches my arm. "Lisa says I have to stick with you."

Thanks, Lisa.

"What? No, I cant. Oh, Lisa, dont ask me that-if I told you, itd do your head in. Its doing my f.u.c.king head in. Jason thinks Im at Mums. No, he doesnt know Im in Germany. Dont tell Dad, will you? Hed only worry-hes as bad as Jason, Dad is. What? No, I told Jason Id be back by half eleven, quarter to twelve. Hes going to go mad when Im not back by then. What am I going to do? Im on a coach being carted off somewhere, I dont even know where. . . ." She starts to cry again. "What? Yeah, all right. Yeah, I will. Just . . . dont say anything to Dad, will you? Cheers, Lisa."

No! No! Dont go, Lisa!

"I have to try to keep calm," Lauren tells me, wiping her eyes. "Easy for her to say. Im not good at being calm. Especially when I dont know where Im going, or how Ill ever get home, if I ever will. Its lucky youre looking after me. If I was on my own, Id go apes.h.i.t."

Tell her. Tell her, now, that youre not looking after her, that you never agreed to do anything of the sort.

"Im stressed, thats what it is," she says. "This is what I get like. Jasons not frightened of anything, he never panics, but me? I lose it when I get stressed, big-time."

I push away a barrage of self-pitying thoughts along the lines of When do I get to cry and physically a.s.sault strangers? and Why cant I be looked after? Ten more minutes of Jason-this-but-I-that might actually make my head explode. Ive already heard that Jason doesnt mind rain and snow, but Lauren hates both; Jason can sleep brilliantly on coaches, but Lauren cant; Jasons good at planning whereas Lauren cant think more than two minutes ahead; Jason knows what to do in a crisis and Lauren doesnt.

And Ive missed another opportunity: failed for the third time to ask her to leave me alone, to make it clear that Im not responsible for her. I should have done it when she fell into my arms sobbing, but I didnt. I should have done it when she rang Lisa the first time, as the coach set off from Dsseldorf Airport, and told her shed made a new friend: a nice middle-aged lady called Gaby who was looking after her. I didnt.

Is Jason intelligent enough to realize that if you describe a thirty-eight-year-old woman as "middle-aged," shes more likely to want to kill you than help you? Because Lauren isnt.

"What am I going to do?" she asks me.

Theres a book in my bag that has magic powers: at least three hundred pages I havent yet read, and the ability to make this all-night coach ordeal bearable. Whats stopping me from getting it out and opening it? Is it my reluctance to discover what "apes.h.i.t" means to somebody whose idea of normal involves wailing in public? If I make the decision to disappoint Lauren, Ill have to suffer the consequences for G.o.d knows how long. There can be no getting away from her until we land in Combingham.

Or do I want her to carry on burdening me with her problems so that sh.e.l.l owe me-so that I wont feel rude when I ask again about the innocent man whos going to prison for murder? Ive already asked about him once, at Dsseldorf Airport. I asked as soon as I humanely could, after Id disentangled myself from our awkward embrace and shed pulled herself together a bit. She clammed up. "Nothing. Forget it," she said. So far, I havent been able to. Perhaps sh.e.l.l let her guard down and bring it up again if I encourage her to talk.

"Jason doesnt know youre in Germany?"

"No. Ive never lied to him before. Four years weve been together. This is the first lie Ive told him. I couldnt tell him the truth."

"Why not?"

"Because I couldnt. Keep your nose out, all right?"

I cant force her to tell me. Although her mouth is at least as much to blame as my nose is. She shouldnt have mentioned her about-to-be-wrongly-convicted acquaintance if she wasnt prepared to share the full story.

I look at my watch. "Its midnight, German time. Eleven oclock in the UK. Youre not going to be back by quarter to twelve."

"I know! Thats what Im saying: Jasons going to go mental."

"What will he do?"

"He thinks Im at my mums. Hes going to ring her, isnt he? Obviously. And shes going to tell him Im not there. Theyll both go off their heads. Believe me, you do not want to see Jason angry. Or my mum, for that matter."

"Which one are you more scared of?" I ask.

She looks at me, puzzled, as if Ive introduced a topic thats unrelated to what we were talking about. "Jason. Im not normally scared of Mum, not unless Ive been taking the p.i.s.s and shes going to find out."

Impatience buzzes in my veins. Im going to have to skip a stage. "Ring your mum," I say. "You havent lied to her yet, so youre still in credibility credit. Youve told her nothing, right? As far as she knows, youre at home with Jason this evening? Ring her now, tell her the truth. Get her to ring Jason and say youre at her house, youve got food poisoning, you cant come to the phone . . . et cetera."

"What do you mean, I havent lied to Mum?" No one else on the coach is speaking at all. Everybody is listening to Laurens shrill voice; its far better at traveling than she is. "Course Ive lied! Ive said Im at her house-how can I tell her that without letting on that Ive lied?"

"You havent lied to her. You havent told her youre at her house, have you?"

Lauren inspects me disdainfully. "Well, I couldnt do that, could I?" she says. "Mums at her house. She knows Im not there. She can see with her own eyes."

Deep breath. "I know that, Lauren. My point is: if you tell her the truth now, confide in her about how youve had to lie to Jason . . ."

"No." She shakes her head vigorously. "Shed ask me why."

Aha. Progress. "And you dont want to tell her?"

"Maybe I could tell her, but not with you right in my face, not with all these people earwigging. Thinking theyre better than me."

"Oh, give it a rest," I snap, before I can stop myself.

"What?"

"Your favorite refrain: 'Everyone thinks theyre better than me. Does the innocent man youre sending to prison think hes better than you?"

"I told you: I dont want to talk about that."

"Oh, sorry," I say casually. "I must have forgotten."

"No," Lauren mutters after a few minutes. "Hes one of the few people who doesnt think it."

And youre rewarding him by letting him go down for murder. Interesting. In the silence that follows, I wonder if I will try to do anything for this unidentified innocent man once I get back to England. Probably not. What could I do: go to the police and tell them what I know? Yes. I could do that. Whether I will or not is another matter. In situations of severe abnormality, I find it hard to imagine what I might do once restored to my normal setting. Sean doesnt understand this. Many times hes berated me over the phone, when Ive been in an airport or a train station or a car hire office, for not knowing if I will or wont want dinner when I get home.

"Its not me sending him to prison," Lauren says sulkily, doing a convincing impression of someone who does, in fact, want to talk about it. "Do I look like the police?"

"Letting him go to prison, sending him there-is there a difference?"

"Yes, there is. Theres a f.u.c.king big difference." She pa.s.ses her phone from one hand to the other and back again.

"Can you stop swearing? Give me that f.a.g packet from your bag-Ill write down twenty new describing words for you to learn."

"Ill do what I f.u.c.king well want, Little Miss Stuck-Up Bossy b.i.t.c.h." She shakes her head. "Sending him to prisond be . . . it would be . . . not the same as . . ."

"Heres what youre trying to say," I chip in helpfully. "Actively doing harm to someone is more morally culpable than failing to step in and prevent harm done by others. Right? The difference between positive and negative responsibility, sins of commission versus sins of omission. Yes?"