Winter in Donegal, and Fin O'Malley is feeling the Christmas blues. Not even a murder can motivate him to return to the police force. When he discovers that the victim is his cousin Raymond, he prefers to stay out of it entirely: he severed ties with his Northern Irish relatives decades ago. It takes a new employee in Caitlin's department to finally spark his ambition. Another victim leads the investigators into the underworld of Derry, where a long-forgotten crime resurfaces. But then the door to Fin's past opens wider than he would like, and his loyalty is put to the ultimate test.