A plot synopsis issued by the BBC in a press release read as follows: "In this drama, a killer has killed once and kidnapped another victim, challenging the investigative and forensic team to work out why.
Kay Rousseau (Louise Lombard), who heads up the crime team, is back at work after the death of her child.
Only Matt Costello (Danny Dyer), Kay's second-in-command and a dedicated, impassioned copper, is loyal to the core.
Dr Clive Morrell (Shaun Parkes) is a profiler whose own mood swings and strange behaviour are causing concern within the team.
Jude Whiley (Lenora Crichlow) is a rookie cop, who is young, fresh and has an energy and passion for the job that verges on obsession.