When Detective Sergeant Lisa Armstrong is assigned to a missing persons investigation, at first it seems like any other – tragic, but all too familiar. As a Family Liaison Officer, she's trained never to get emotionally involved. Her job is to support families during the worst time of their lives whilst also to be the eyes and ears of the police investigation; a cuckoo in the nest.But there's something very different about this particular case. With horror Lisa realises she's got a personal connection with this frightened family; one that could compromise her and the investigation.As she grapples to get justice for the grieving family, Lisa discovers it could come at a cost.

When the main suspect goes missing, Lisa is concerned about Sean's possible involvement. The discovery of a key piece of evidence provokes a number of new theories and the police begin to look more closely at other members of the Meredith family. Abbie falls deeper into Vincent's world, bringing Sam with her. Meanwhile, Sean's vigilante justice leads him down a dangerous path.