It's every parent's worst nightmare - your child abducted and murdered. Their body found hundreds of miles away.

For Andy Cardy this was a shocking reality. After his nine-year-old daughter Jennifer disappeared in Northern Ireland in 1981, the entire local community banded together in an effort to find the little girl. Days later, Jennifer's body was found floating in a dam over 10 miles from where she went missing. With no leads or clues, the trail for her murderer went cold. But nobody could have predicted this was the work of a disturbing serial killer.

Over the next five years, three more young girls were snatched from plain view – vanished, in a matter of minutes. The tragic discoveries of their bodies, days - sometimes weeks - later, suggests the work of a calculated, sadistic, travelling predator.

Detectives from multiple forces attempt to join the dots between these child murders using antiquated policing systems. Police technology is in its infancy - without vehicle registration recognition, CCTV, or even fully-fledged computer systems - can they close the net before the killer strikes again?

A devastating impact is left on the families of these victims - Jennifer Cardy, Susan Maxwell, Caroline Hogg and Sarah Harper. Parents who'd expected to see their daughters again are now left hoping for justice.

As the years tick by and hundreds of suspects are eliminated, it feels inevitable that another child will be snatched. But could a stranger-than-fiction arrest in a quiet rural village, after a local officer makes an appalling discovery, prove pivotal in the case? Will this serial killer of children ever be caught?