After a harrowing experience, DC Dinah Kowalska learns she’s on the shortlist for a promotion from her no-nonsense boss, DI Vivienne Deering. Later, Dinah connects a body at the morgue to a series of murdered girls with Down’s syndrome.

Dinah invites Cathy, the girl she saved, to stay at her house, but their arrangement causes trouble for the investigation. After watching a teenager overdose, Viv and her team trace a bad batch of drugs to a wealthy couple.

The squad crashes the wedding of a neo-Nazi to charge him with a firebombing that killed a Pakistani woman. When the suspect claims to have an alibi, Dinah and her colleague DS Joy Freers believe the arson may not have been a hate crime.

Dinah attends to a man who walked out in front of a car to commit suicide, but the case becomes more complicated when the police inform the next of kin. Viv’s team desperately searches for a missing girl, concerned she may be the serial killer’s next victim.

Police respond to a stabbing and discover that the victim has a secret identity. Having connected the serial killer to an online dating site, Forensics Officer Miller poses as a teenage girl to lure the culprit, while Dinah tries to mend her broken relationship with Cathy.

As Viv frantically chases down Cathy’s attacker, the squad makes a startling realization. When the pursuit doesn’t go as planned, Viv’s team stumbles upon a seriously injured young man. Meanwhile, Dinah has doubts about the serial killer investigation.