Nicolai thanks the good doctor, said his goodbyes, settled his bill, and was gone--but not for long.
Because this place was perfect.
He was back within the week after spending a couple days scoping out the place, getting an idea of Rook and Tawny's habits. He observed that Tawny tended to leave earlier than Rook, but Rook's habits varied. Sometimes he left on time, and sometimes he stayed after hours. Mornings, however, were more consistent; he arrived an hour before opening and Tawny arrived at opening. He also observed the traffic around the area, how busy the Cancer was in this part, and checked out all the entrances and exits to the place--not necessarily the official entrances, but there was a back door.
He waited several days to make sure the pattern he'd observed was reliable.
Finally, the day came and he was up bright and early. He got to the office an hour before Rook did, picked the lock, secured the door behind him, and made his way inside the office to wait for him in the dark.