When the Police Service of Northern Ireland are unable to close a case after 28 days, Detective Superintendent Stella Gibson of the Metropolitan Police Service is called in to review the case. Under her new leadership, the local detectives must track down and stop a serial killer who is terrorising the city of Belfast.
Stella Gibson has finally arrested Paul Spector, but he has been shot by jealous husband James Tyler, leaving the staff at Belfast General Hospital battling to save his life. As the shooting hits the news, the powers-that-be question Gibson's handling of the case, while Spector's young partner-in-crime Katie plots to help him.
Gibson and Burns are hauled over the coals by the Police Ombudsman and the Policing Executive for their conduct and handling of the case. When Spector’s name is released to the press as the arrested suspect in the Belfast Strangler case, his wife and family are forced to deal with the consequences.
Spector's legal team move into action, determined he won't stand trial.
Gibson comes face to face with the depths of Sally-Ann's desperation.
Spector's legal team are determined that he will never stand trial. Anderson and Ferrington make a discovery from the past that may help Gibson build her case.
The series concludes as Gibson and Anderson put fresh evidence to Spector, with explosive results. Spector's new-found friendship with another inmate develops, with devastating consequences.