When an immigrant is found tortured and murdered in a ritualistic killing, Beckett navigates the uncharted territory of the mysterious Vodun religion with Castle leading the way. Having researched similar deaths for one of his books, Castle's knowledge and sources prove valuable, but only their apt teamwork can unravel the murderer's motives. Meanwhile, Castle is confronted with the possible return of his first wife, Alexis's mother, whose dizzying personality threatens to upend the tranquility of the entire family.

Castle and Beckett investigate the murder of a woman found drowned in a bathtub of motor oil at a transient hotel. But when they uncover a dark secret about the woman's past, they must unravel a 20-year-old mystery with the help of a true crime journalist who may have been stalking the victim. Meanwhile, Beckett puts her poker face to the test as she squares off against Castle, with her money and pride at stake.