Sam Ryan embarks on a journey home to Northern Ireland when the team is called out to investigate the discovery of the bodies of two men killed by paramilitaries twenty years ago and finds that their secrets live on in the new corridors of Belfast power.

Now Sam has left, Leo is faced with the decision of whether to take over her job; meanwhile he and Harry clash over an investigation into an outbreak of disease among school children on the South Coast. Then together they investigate an apparent case of Munchausens by proxy and race against the clock to prevent a potentially fatal environmental disaster.

When members of a syndicate owning a prize race horse are killed in a helicopter crash Leo and Harry investigate a complex betting scam; meanwhile the mortuary finds itself with an unconventional new member of staff. New girl Nikki joins the team as Harry finds himself implicated in a corrupt officer's enthusiasm to get his conviction while Leo investigates a cash-for-transplants ring.

The team is approached by a support group of survivors from a recent train crash. What caused the tragedy, and what is the identity of the unidentified Body 21? When the mysterious body is named, Harry, Nikki and Leo get closer to finding out what caused the train crash - with tragic consequences for one of the heroes of the disaster.

Harry is called out to a death at a racecourse where a jockey's horse crushed him to death.

Matt Gibb, another member of the syndicate, becomes the prime suspect when police discover he has huge gambling debts.

Leo and his team are approached by a support group to help discover the truth behind a train crash.

Leo, Harry and Nikki step up their efforts to discover the truth behind the train crash but there are still many unanswered questions.