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.

A shootout at a City hotel leaves young Ukrainian nanny Sofia Teplov dead, along with an unknown hitman. The Russian oligarch target Maksim Bazhanov narrowly escapes. Nikki and Jack work with young City DI Sarah Parks to ascertain the identity of the dead hitman and find out who is trying to kill Bazhanov and why.

Jack is drawn to Sarah, impressed by her ability to juggle work and family when he finds out her daughter has a rare childhood cancer. The discovery of the hitmen's identities as ex-army frustrates the team when they realise they could have been hired by any number of paymasters.