Sam, Leo and Harry travel back to Sam's old home in Northern Ireland when two bodies are discovered there. As events unfold, Sam realises her father may have been involved and sets out to discover the truth.

Now Sam has left, Leo is faced with the decision of whether to take over her job as Professor. Meanwhile he and Harry clash over an investigation when they look into an outbreak of disease among school children on the South Coast.

When members of a syndicate owning a prize race horse are killed in a helicopter crash Leo and Harry begin to investigate, and an unexpected new face at the mortuary lends a helping hand.

The team are approached by a support group of survivors from a recent train crash, who want them to investigate what happened. They agree and begin to look into how the crash occurred, and the identity of the unidentified Body 21.