On a sunny morning in June, Margaret Carpenter wakes up to find a new iPhone on her doorstep. She switches it on to find a text from her best friend, Charity Atwater. The problem is, Charity's been missing for over a month. Most people in town--even the police--think she's dead.

Margaret and Charity have been lifelong friends. They share everything, know the most intimate details about one another...except for the destructive secret hidden from them both. A secret that will trigger a chain of events ending in tragedy, bloodshed, and death. And now Charity wants Margaret to know her story--the real story. In a narrative that takes place over one feverish day, Margaret follows a series of increasingly disquieting breadcrumbs as she forges deeper into the mystery of her best friend--a person she never truly knew at all...