At twenty-six, Dahlia Lighthouse is haunted by her upbringing. Raised in a secluded island mansion deep in the woods and kept isolated by her true-crime-obsessed parents, she is unable to move beyond the disappearance of her twin brother, Andy, when they were sixteen. Following her father’s death, Dahlia returns to the house, where the family makes a gruesome discovery; buried in their father’s plot is another body-Andy’s. Dahlia is quick to blame Andy’s murder on the serial killer who terrorized the island for decades, but as she grapples with her own grief and horror, she realizes that her eccentric family, and the mansion itself, may hold the answers to what happened to her twin.