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.