"Superintendent Sandra Pullman ... heads a team of aging detectives pulled out of retirement for a job they're uniquely qualified to do: tackle cold cases--some of them decades old"--Container.
Harry and Nikki's tentative new relationship is jeopardized when Harry's ex-girlfriend is killed. Nikki takes on the case, which looks like suicide, but Harry becomes obsessed. Meanwhile, Leo works on the elaborately staged murder of conceptual artist Jimmy Triangle.
Memories of his own daughter's death are stirred when Leo is called in to investigate the suicide of a young girl. Confusion arises when the case is linked to that of a car salesman. Meanwhile, Nikki investigates the death of an elderly woman.
A group of strangers, each at a crossroads in their lives, are brought together at a Scottish estate for another chance at love, friendship, and forgiveness.
When four bodies are found in the Thames after a boat filled with illegal immigrants is wrecked, the team realize they are dealing with a people trafficking operation. They set out to look for survivors and find themselves delving into communities of illegal immigrants.
Harry finds himself in the middle of a dangerous cover-up and has to work against the clock to find those responsible. Meanwhile, Lionel's hearing continues, and Leo will eventually have to decide whether to follow his conscience, and betray his old friend and mentor.
Harry investigates a hit and run accident on a rundown council estate while Leo is drawn into the case of a woman killed in a terrible and suspicious fire at her house. Nikki examines a woman who collapsed and died on her hen night.
Leo investigates a drunk who died on a night bus, Nikki investigates the poisoning of a go-ahead sales executive, and when Harry is called out to the apparent suicide of a premier league football star he uncovers a link back to the accident at the housing estate.
Leo is puzzled by more contrary clues in the strange death of conceptual artist Jimmy Triangle. Someone is playing a game, but who and why? Meanwhile, Harry and Nikki are pushed further apart when he forces her to re-examine the body of his ex-girlfriend.
Leo races to find a connection between two apparently motiveless murders as a third killing takes place at a school and the police decide they are looking for a serial killer. Nikki, meanwhile, proves that her elderly victim did not die as a result of being attacked.
The discovery that one of the bodies from the wrecked boat in the Thames was carrying a highly infectious disease increases the pressure on the team to track down any other survivors before the virus breaks out into the wider community.
Harry and Nikki are called out to a dog sanctuary where the body of a teenage girl has been found. Meanwhile, Leo is called to the General Medical Council as a character witness for his mentor, Professor Lionel Clune.
