He sees it, too. In his quieter moments. Sure, he's been on the line with Beckett in the past -- that's part of the job (well, it's part of her job and he's insinuated himself right there alongside her) -- and there've been a few heart-in-throat moments where one or both of them would have probably come out on the wrong side of the equation if they hadn't been very lucky.

Coonan had been different.

He remembers losing track of the guy for a second (just a second; barely a blip on the radar) and then feeling the greasy muzzle of a gun digging into his scalp. Beckett's in front of him, her body squared in an Isosceles firing stance, tight as a piano wire. Pop! Pop! Pop! Who's playing with fireworks in the precinct? And Coonan's weight slumping down, Castle's arms free, his foot scudding fecklessly on the tile. Red tile.

Castle closes his eyes.

"I don't know," he whispers.

He draws his arm around her shoulder, folding her toward his chest.