Bellatrix Black/Severus Snape
It was surprising how much being in the crowded hall made him melancholy. The last two years of his life had been particularly horrific, of course, but prior to that time he had quite enjoyed teaching, living at Hogwarts, feeling useful and involved in something important outside his own miserable existence. He needed to get away from the throng for a bit to regain his bearings. Considering that the castle wasn't Hogwarts, not even close to her size and scale, it didn't take too many twists and turns of corridors to settle his grief and regret back to something that was just a dull ache, easily ignored for the present.
Something else occurred to quickly remind him of his teaching days at Hogwarts, and this not in a sorrowful way but a rather delightful one. He'd enjoyed catching the little toerags in various misdeeds and now he had opportunity to reprise that role a bit.
"I believe that door was closed for a reason, Miss Black," he said mildly as he caught sight of her in an alcove, trying a latch that appeared to be locked. "Were you tired of the feast?"