In a quiet caravan park on a summer's afternoon a seveN-year-old boy goes missing. Miles away -in a seemingly unconnected case - another seven-year-old boy is also reported missing - taken from a children's play area. These incidents at first appear random, until it emerges that the boys live in the same area.

Barclay (Hugh Bonneville) and his team, including fast-tracked DI Zoe Larson (Eleanor Matsuura) and experienced officer DS Nick Dyer (Geoffrey Streatfeild), struggle to find links between the boys, or clues to their whereabouts. They are increasingly hampered by the force's senior management and a home office determined not to negotiate with the kidnappers.

Frustrated at the speed of events and the team's lack of progress Barclay calls upon his old colleague and trusted friend Amy Foster (Janet McTeer) to help.