Courtney Summers’ latest book, Sadie, is a dark new thriller fusing episodes of a true crime podcast focusing on the disappearance of small-town girl Sadie with the first-person story of Sadie herself, on a desperate mission of vengeance following the abduction and murder of her younger sister. Summers’ books explore the darkest things that can happen to girls, from sexual assault to ostracization to supernatural attack. Her heroines are flawed and fascinating, her depiction of their struggles unflinching. We talked to her about her process, her fandoms, and why she goes dark.