When four bodies are found in the Thames after a boat packed with illegal immigrants crashes, the team realise that they are dealing with a people-trafficking operation gone wrong. As they set out to discover whether there are any survivors or other bodies – and try to track down those responsible – Harry, Nikki and Leo gradually learn more about the victims' tragic stories. The dead are a Chinese couple who were fleeing their home because they weren't allowed to have a second child, an African political activist and a young Albanian man whose brother was granted asylum.As they get closer to the Chinese gang behind the operation, Nikki comes to realise that the Chinese couple's six-year-old daughter may still be alive on the Thames marshes.

Harry is joined by Sergeant Susan Fenn to investigate a hit-and-run accident on a run-down council estate. Leo and arch-cynic DI De Rohan are drawn into the case of a woman killed in a terrible fire at her house. And Nikki examines the body of a woman who collapsed and died at her own hen night.

Harry's ex-girlfriend, Penny Harris, is found dead after an unusual car accident. Nikki takes on the case – which initially looks like suicide – while DCI Ambrose learns that Penny may have been having an affair. Nikki's post mortem produces a devastating revelation for Harry. Leo works on the elaborately staged apparent suicide of conceptual artist Jimmy Triangle. An anonymous video puts art critic Seth Jewell in the frame. But Leo isn't convinced and he starts to realise that this death is an artwork in its own right.

Memories of his own daughter's death are stirred up when Leo is called in to investigate the apparent suicide of a 14-year-old girl, Alison Garland. With the help of child psychologist Caroline, Leo realises that Alison was, in fact, murdered. But they are stumped when the killing is linked to Harry's case, in which a car salesman has been stabbed to death apparently with the same knife. As Leo gets deeper into the unfamiliar teenage world he starts to suspect the school rebel, Fish – but is there another connection? Nikki investigates the death of elderly woman Kay, who appears to have been assaulted by an intruder. While Kay's son, Robert, demands justice, Nikki finds that the truth is more surprising.

Harry and Nikki are called out to a London dogs' home where the naked body of a teenage girl has been found, tortured to death. It becomes clear that a second girl is being held somewhere, the pathologists find themselves pulled into a world of violence, spies, extremism and cover-ups.

Harry and Nikki are called out to a London dogs' home where the naked body of a teenage girl has been found, tortured to death. It becomes clear that a second girl is being held somewhere, the pathologists find themselves pulled into a world of violence, spies, extremism and cover-ups.