ITV go through every step of the police investigation, in a crime described by prosecutor John McDermott QC as one of "demonic savagery". This one-off doc follows lead Detective Paul Withers as he works with his team in the Lancashire Police to uncover the mystery behind the ‘targeted and ferocious’ attack on Hartley. The 90 minute special covers the entire story up until the conviction of killers Sarah Williams and Katrina Walsh.