Unforced Error

Harry Potter Fanfiction
Hermione Granger finds herself locked in a room together with the last person she'd expect...her former Potions Professor. It quickly becomes apparent that the room has very unusual properties and that Snape knows much more than he's letting on. Unfortunately for him, Hermione is very good at getting answers. Canon-divergent starting from the horcrux hunt in book 7.
Hermione/Severus