So I registered nothing.
It is not my job to wonder why.
I have replayed that dinner in my memory more times than I can count, looking for the moment I should have known something was wrong, and the truth is that there was no such moment, not really.
They were good at it.
That is what professionals are, after all: good at being unremarkable, at blending into the ordinary texture of a room, at watching without appearing to watch.
The only thing my instincts snagged on all night was that faint quality of attention, that sense that their focus was not quite where it should have been, not on each other, not on the food, but somewhere in the periphery, on the doors, on the room, on me.
And even that I explained away, because you have to explain such things away to do this job; you cannot treat every strange customer as a threat or you would go mad.
So I brought them their wine and their steaks and their check, and I never once suspected that the odd couple in my section had come not to dine but to confirm, with their own eyes, that the waitress serving them was the woman a downtown law firm had spent six months and a small fortune trying to find.