I know this fic has been rec'd before. I'm sure that it has. But if you haven't seen a rec on it now, know that I love this.
I'm reading it slowly. My first inclination is to devour it all down, but it's soooo good, it needs to be savored. The Potion Mistress has blown me away. It's chilling. Her Hermione plot is fascinating and scary. But her Severus. Oh my. Gritty, real, and so perfectly in character.
You must go read it. Read the Prologue first.