De Costa is roped in when the father of a young Ugandan girl asks for help in tracing her after she disappears whilst in the care of another family. When she and Perkins find the young girl locked away in the attic of a suburban house, they suspect that the girl is just one of a number who have been trafficked by the householders. DCI Caddick of the Child Abuse Investigation Team arrives to assist with the case and is impressed with De Costa's ability to build links with the immigrant community. Meanwhile, Hunter and Masters investigate a robbery where the supposed robber has left his wallet behind at the scene - but surely nobody can be careless enough to leave a calling card?