Sirius stepped from the grate and smoothly to one side to make room for Harry. He seemed to be early; the only other arrival was-- His pulse quickened, and not in the good way. Severus Snape. What were the odds?
Ignoring the man, he stepped forward, and determined to be on his best behavior, took Minerva's hand and raised it for the polite suggestion of a kiss. "Professor McGonagall. So good to see you again." With Gaius not in mortal danger, yet.