Demons in the Architecture

Velia Bagshot is a muggle-born, but due to her sharing the last name of author Bathilda Bagshot, she's always passed as a pure-blood. But what happens when a deceased teacher who is oblivious to the tense climate sets an assignment instructing students to explore their partner's family history? And what happens when her partner is the dark wizard Regulus Black? RB/OC plus RL