Susie Nightingale is more than ready to stand up to Coulson as the funeral of Inspector Briggs forces everyone to decide where their loyalties lie. Annie and Inspector Sawyer are running out of time to get to the bottom of the Petra Project. Others are taking a more direct approach to justice.

Coulson reasserts control at the station and exacts retribution on Briggs. Details begin to emerge about horrific medical experiments carried out on twins in the Nazi death camps and about a secret mission involving the murdered brigadier. The investigation focuses on the Edmund Hall psychiatric hospital.

Annie suspects the key to the case lies in special operations conducted during the war, but her father is reluctant to share his experiences with her. She also gets to play matchmaker at the station. Meanwhile, another relationship is coming to an end, though not soon enough to save the career of a fellow officer.

Annie's involvement in a gruesome murder case causes a rift with her father. Fenton worries he is no longer up to the job.

New arrival WPC Annie Taylor goes on a hunt for a predator who is targeting contestants in a local beauty contest. At the station, some old faces remain, with Assistant Chief Constable Coulson refusing to step down and Sergeant Fenton back from leave after his shooting. Matters escalate when a masked gunman appears at the home of a contest attendee.