"She's a detective," Frank said, very gently.

"Yeah," Sam said, after a long moment. He let the front legs of his chair down again, carefully. "She is." His eyes skated away from Frank, across the squad room: empty desks in dimming corners, the explosion of scribbles and maps and Lexie on the whiteboard, me.

"Don't look at me," O'Kelly said. "Your case, your call." If this thing went splat, and he obviously thought it would, he wanted to be well out of range.

All three of them were starting to get right up my nose. "Remember me?" I inquired. "You might want to start trying to convince me, too, Frank, because I'd say this was at least partly my call."

"You'll go where you're sent," said O'Kelly.

"It is, of course," Frank told me reproachfully. "I'm getting to you. I felt it would be polite to start by discussing matters with Detective O'Neill, what with this being a joint investigation and all. Am I wrong?"

This is why joint investigations are from hell: nobody is ever quite sure who the big boss is, and nobody wants to find out. Officially, Sam and Frank were supposed to agree on any major decisions, but if it came to the crunch, anything to do with undercover was Frank's call. Sam could probably override him, since this had started out as his investigation, but not without an awful lot of string-pulling and a damn good reason. Frank was making sure--I felt it would be polite--that Sam remembered that. "You're dead right," I said. "Just remember, you need to discuss matters with me, too. So far, I haven't heard anything very convincing."

"How long are we talking about?" Sam asked. He was asking Frank, but his eyes were on me, and the look in them startled me: they were intent and very grave, almost sad. That was the second when I realized Sam was going to say yes.

Frank saw it too; his voice didn't change, but his back had straightened and there was a new spark in his face, something alert and predatory. "Not long. A month, max. It's not like we're investigating organized crime and we could need someone on the inside for years. If this doesn't pay off inside a few weeks, then it's not going to."

"She'd have backup."

"Twenty-four-hour."

"If there's any indication of danger--"

"We'll pull Detective Maddox out straightaway, or go in and get her if we need to. Same if you develop information that means she's no longer necessary to the investigation: we'll have her out that same day."

"So I'd better get cracking," Sam said quietly, on a long breath. "OK: if Detective Maddox wants to do it, then we'll do it. On condition that I'm kept fully informed of all developments. No exceptions."

"Beautiful," Frank said, sliding off his chair fast, before Sam could change his mind. "You won't regret it. Hang on, Cassie--before you say anything, I want to show you this. I promised you videos, and I'm a man of my word."