The loft
It's interesting how Debbie and Brian both protest the injustice in opposite ways...Debbie by going home and going big, raising an uproar, and Brian by slipping under the radar and delivering personal retribution.
Brian asks Michael when he's going back, knowing perfectly well what the answer is.
M: Maybe that's the problem. I don't know where the fuck I belong. B: *kisses him* There, that's where.
Then the chemistry book...of course Brian has a plan.