The light through the curtains glinted blue on his glasses as he turned his head to me. “Who are you?” he asked.

I thought as fast as even Frank could ever want from me, I already had one finger on my mouth to shut him up while my other hand smacked the light switch, and then I called, “Hey, it’s me, I’m out here,” and thanked God Daniel was weird enough that we might just possibly get away with that Who are you? His eyes were intent on my face, and he was between me and my case. “Where is everyone?” I asked him, and ripped open the buttons of my top so he could see the tiny mike clipped to my bra, the wire running down into the white pad of bandage.

Daniel’s eyebrows lifted, just a touch. “They went to see a film in town,” he said calmly. “I had a few things I needed to do here. We decided not to wake you.”

I nodded, gave him the thumbs-up and knelt down slowly to pull my case out from under the bed, not taking my eyes off him. The music box on the bedside table, solid and sharp-cornered and within reach: that should slow him down long enough to get me out of there if I needed it. But Daniel didn’t move. I dialed the combination, opened the case, found my ID and threw it to him.

He inspected it closely. “Did you sleep well?” he asked formally.

He had his head bent over the ID, apparently absorbed in it, and my hand was on the bedside table, inches from my gun. But if I went to slip it into my waistband and he looked up; no. I zipped the case shut and locked it. “Not great,” I said. “My head is still killing me. I’m going to go read for a while and hope it gets better. See you in a bit?” I waved a hand to get Daniel’s attention; then I moved towards the door and beckoned.

He gave my ID one last look, then laid it carefully on the bedside table. “Yes,” he said. “I’m sure I’ll see you later.” He got up from the bed and followed me downstairs.

He moved very silently, for such a big guy. I could feel him at my back all the way and I knew I should be scared-one push-but I wasn’t: adrenaline was flying through me like wildfire and I’ve never been less afraid in my life. Rapture of the deep, Frank called it once, and warned me not to trust it: undercovers can drown like deep-sea divers on the ecstasy of weightlessness, but I didn’t care.

Daniel stood in the sitting-room doorway, watching me with interest, while I hummed “Oh, Johnny, How You Can Love” under my breath and flipped through the records. I picked out Fauré’s Requiem, stacked it up over the string sonatas-Frank might as well have something good to listen to, broaden his cultural horizons, and I doubted he’d notice the midstream switch-and turned it up to a nice solid volume. I flopped into my chair with a thump, sighed contentedly and flipped a few pages of my notebook. Then, very carefully, I peeled off the bandage strip by strip, unclipped the mike from my bra, and left the whole package on the chair to listen to music for a while.

Daniel followed me through the kitchen and out the French doors. I didn’t like the idea of crossing the open lawn-You won’t have visual surveillance, Frank had told me, but he would have said that either way-but we didn’t have a choice. I skirted around the edge and got us in among the trees. Once we were out of view, I relaxed enough to remember my buttons and do them up again. If Frank did have someone watching, that would have given him something to think about.

The alcove was brighter than I had expected; the light slanted long and gold across the grass, slipped between the creepers and glowed in patches on the paving stones. The seat was cold even through my jeans. The ivy swayed back into place to hide us.

“OK,” I said. “We can talk, but keep it down, just in case.”

Daniel nodded. He brushed flecks of dirt off the other seat and sat down. “Lexie is dead, then,” he said.

“I’m afraid so,” I said. “I’m sorry.” It sounded ludicrously, insanely inadequate on about a million levels.

“When?”

“The night she was stabbed. She wouldn’t have suffered much, if that’s any comfort.”

He didn’t respond. He clasped his hands in his lap and gazed out through the ivy. At our feet the trickle of water murmured.

“Cassandra Maddox,” Daniel said eventually, trying out the sound of it. “I wondered quite a lot about that, you know: what your real name was. It suits you.”

“I go by Cassie,” I said.

He ignored that. “Why did you take off your microphone?”

With someone else I might have skated around this, parried it-Why do you think?-but not with Daniel. “I want to know what happened to Lexie. I don’t care whether anyone else hears it or not. And I thought you would be more likely to tell me if I gave you a reason to trust me.”

Either out of politeness or out of indifference, he didn’t point out the irony. “And you think I know how she died?” he inquired.

“Yes,” I said. “I do.”

Daniel considered this. “Shouldn’t you be afraid of me, in that case?”

“Maybe. But I’m not.”

He scrutinized me for a long moment. “You’re very like Lexie, you know,” he said. “Not only physically, but temperamentally as well. At first I wondered if I simply wanted to believe that, to excuse the fact that I had been fooled for so long, but it’s true. Lexie was fearless. She was like an ice skater balanced effortlessly on the edge of her own speed, throwing in joyous, elaborate twirls and leaps just for the hell of it. I always envied her that.” His eyes were in shadow, and I couldn’t read his expression. “Was this just for the hell of it? If I may ask.”

“No,” I said. “At first I didn’t even want to do it. It was Detective Mackey’s idea. He thought it was necessary to the investigation.”

Daniel nodded, unsurprised. “He suspected us from the beginning,” he said, and I realized that he was right; of course he was right. All Frank’s talk about the mysterious foreigner who followed Lexie halfway across the world, that was just a smoke screen: Sam would have thrown a blue fit if he thought I was going to share a roof with the killer. Frank’s famous intuition had kicked in long before we ever got into that squad room. He had known, all along, that the answer was in this house.

“He’s an interesting man, Detective Mackey,” Daniel said. “He’s like one of those charming murderers in Jacobean plays, the ones who get all the best monologues: Bosola, or De Flores. It’s a pity you can’t tell me anything; I would be fascinated to know how much he’s guessed.”

“So would I,” I said. “Believe me.”

Daniel took out his cigarette case, opened it and politely offered it to me. His face, bent over the lighter as I cupped my hand around the flame, was absorbed and untroubled.

“Now,” he said, when he had lit his own smoke and put the case away, “I’m sure you have some questions you’d like to ask me.”

“If I’m so much like Lexie,” I said, “what gave me away?” I couldn’t help it. It wasn’t professional pride or anything; I just needed, badly, to know what that unmissable difference had been.

Daniel turned his head and looked at me. There was an expression on his face that I hadn’t expected: something almost like affection, or sympathy. “You did extraordinarily well, you know,” he said, kindly. “Even now, I don’t think the others suspect anything. We’ll have to decide what to do about that, you and I.”

“I can’t have done all that well,” I said, “or we wouldn’t be here.”

He shook his head. “I think that underrates both of us, don’t you? You were virtually flawless. I did know, almost immediately, that something was wrong-all of us did, just as you would sense something amiss if your partner were replaced by his identical twin. But there were so many possible reasons for that. At first I wondered if you might be faking the amnesia, for reasons of your own, but gradually it became clear that your memory was, in fact, damaged-there seemed to be no reason why you should pretend to forget about finding that photo album, for example, and it was obvious that you were genuinely disturbed by the fact that you didn’t remember it. Once I was satisfied that that wasn’t the problem, I thought perhaps you were planning to leave-which would have been understandable, in the circumstances, but Abby seemed very sure that you weren’t, and I trust Abby’s judgment. And you really did seem…”