As the police investigate the possibility of a copycat killer among the students, a friend from the college pressures Sam to put loyalty above the truth as the case unfolds.
The murder of a probation officer leads the team to the doorstep of a police cadet college, as they quickly establish a link to a similar murder just months before.
A new murder turns DCI Ashton's suspicions toward the victim's family and friends, whilst Harry investigates a death that may be linked to the Irons family.