"I'm not trying to get into an argument," I said. My knees were shaking and I had no idea how we had ended up fighting about this, when we were basically on the same side. "Just . . . leave it, OK? Please, Sam. I'm asking you."

"Cassie," Sam said. His round, pleasant face had a look of anguish that didn't belong there. "I can't do this. What if . . . God. What if something happens to you? On my case, that had nothing to do with you. Because I couldn't bloody well get my man. I can't live with that. I can't."

He sounded breathless, winded. I didn't know whether to hold him tight or kick him. "What makes you think this has nothing to do with me?" I demanded. "This girl is my double, Sam. This girl was going around wearing my fucking face. How do you know your guy got the right one? Think about it. A postgrad who spends her time reading Charlotte bloody Bronte, or a detective who's put dozens of people away: who's more likely to have someone out to kill her?"

There was a silence. Sam had worked on Operation Vestal, too. Both of us knew at least one person who would happily have had me killed without a second thought, and who was well able to get the job done. I could feel my heart banging, hard and high under my ribs.

Sam said, "Are you thinking--"

"Specific cases aren't the point," I said, too curtly. "The point is, for all we know I could be involved up to my tits already. And I don't want to be looking over my shoulder for the rest of my life. I can't live with that."

He flinched. "It wouldn't be for the rest of your life," he said, quietly. "I hope I can promise you that much, at least. I do plan to get this fella, you know."

I leaned back against the counter and took a breath. "I know, Sam," I said. "I'm sorry. I didn't mean it that way."

"If, God forbid, he was after you, then all the more reason to stay out of the way and let me find him."

The cheerful cooking smell had grown an acrid, dangerous edge: something was starting to burn. I switched off the cooker, shoved the pans to the back--neither of us was going to feel like eating for a while--and sat down cross-legged on the sofa, facing Sam.

"You're treating me like your girlfriend, Sam," I said. "I'm not your girlfriend, not when it comes to this kind of thing. I'm just another detective."

He gave me a sad, sideways little smile. "Could you not be both?"

"I hope so," I said. I wished I hadn't finished the wine; this man needed a drink. "I really do. But not like this."

After a while Sam let out a long breath, let his head fall back against the sofa. "So you want to do it," he said. "Mackey's plan."