Webb and Perkins investigate the disappearance of two young schoolgirls, concerned that their disappearance may be linked to the Amy Tennant case. As uniform begin a frantic search for the missing youngsters, Hemmingway and Bryant find them cowering in fear in the depths of a dark underpass. With the younger of the two siblings, Molly, having been beaten across the head, the search begins for their attacker - and the team are soon track down their prime suspect, a local waterworks employee who was seen with the two children shortly before the attack. However, forensic analysis shockingly reveals the older sibling's fingerprints on the weapon used to bludgeon her sister.