DCI Cassie Stuart and DI Sunil 'Sunny' Khan reunite to solve another historical crime, their first since they chose to walk away from a case in which victims of child sex abuse had worked together to murder their abusers. This new investigation sees four men under scrutiny when the body of a teenage girl is found at a building site off the M1 motorway. It's revealed that she's been missing since the turn of the millennium and it's up to Cassie and Sunny to figure out whether any of the men had anything to do with her death.