John Yesterday has walked the earth for centuries, an immortal man whose endless existence remains inexplicable—until a chance discovery reignites questions he thought long buried. When he and his girlfriend Pauline, who together deal in obscure antiquities, stumble across a connection to an ancient tome known as the Book of the Flesh, they find themselves chasing threads that span from the Spanish Inquisition to the present day. The investigation pulls them backward through time to uncover how John first attained immortality with the help of a sympathetic priest named Father Ginés, while simultaneously forcing them to confront dark truths about the curse that has defined his centuries-long existence. As past and present intertwine, the couple must piece together the real price of John's deathlessness and the forces that set his immortal journey in motion.