What are you, a dog?

Written for a prompt on the new kink meme, at hpkinkmeme on Dreamwidth. Lucius, on a visit to some of the older Slytherins still at Hogwarts, comes across Sirius Black in the corridors, and allows himself an indiscretion. Rated M. Note that this is a non-explicit version of the complete work, which at 6k is on Ao3 in its entirety.