Septima's ears weren't as good as they once were, but she wasn't so terribly old for a witch, and she thought she could hear breathing in the darkness. Cautiously, she backed up until her back was against one of the stone walls.
With a quick incantation, she illuminated the classroom, leaving her blinking into the sudden brightness, and held out her wand. Hopefully whoever was there would be blinded as well.
Her eyes stinging, she squinted for anything that might be a threat.