Detective Sergeant Nancy Devlin (Karla Crome, Under the Dome, Prisoners' Wives) is a good cop with a dark secret: she's loyal to drug trafficker Frank Le Saux (Philip Glenister, Life on Mars, Ashes to Ashes), who is like a father to her. But when their clandestine meeting turns violent, leaving Frank dead and Nancy with a bullet wound, Nancy fears her double life may soon be exposed. Assigned to Brighton to investigate the crime, Nancy must track down Frank's killer while concealing her role-and her injury-from her enigmatic new partner, DS Gunner Martin (Noel Clarke, Star Trek Into Darkness), and her old friend, DS Kevin O'Dowd (Robert James-Collier, Downton Abbey). Can Nancy stay one step ahead of her colleagues-and the killer?