Atonement

Hermione saves Sirius in the Department of Mysteries—but at the cost of a death eater's life. As she struggles to reconcile her actions, Bellatrix Black, the Dark Lord's greatest lieutenant, develops a dangerous, unrelenting interest in her. What follows is a series of unprecedented events, unlikely mentors, and Hermione's own fracturing sanity. / Hermione-centric / Snape Mentor