When suspected paedophile Dale Barge is found murdered in a children's playground, Nikki and Jack are brought in by inexperienced detective Rory Drennan. It's not long before the team link Barge's death to a missing child, Lizzie Craddock. Jack teams up with hard-nosed child protection DI Gina Conroy. They put pressure on Lizzie's parents Johnnie and Cheryl to try to find her. Lizzie's social worker Louise is brought in to help, and Nikki encourages her to stay positive when she blames herself for Lizzie's disappearance.