The case of the murder of an enforcer for an Irish gang takes a personal turn when Lanie and a forensic expert friend of Castle's uncover an undeniable connection between the case and Beckett's mother's unsolved murder. The trail leads to Dick Coonan, a philanthropist by day and an assassin known as "Rathborne" by night. Coonan murdered Johanna Beckett, but he takes Castle hostage and Beckett is forced to shoot him before she can learn who paid him to kill her mother.