While investigating a suspicious death in a prison, Nikki focuses her attention on the victim’s cellmate, a dangerous criminal from her past.

As the team investigate a second death, Nikki’s theory starts to fall apart. Can she put her fixation with Scott aside and find the killer?

In the first case for new recruit Adam, the murder of a swimming instructor leads the team to suspect her ex-boyfriend, a former cop. Meanwhile, Jack has an unexpected visitor.

Having traced Laura’s last movements to a suburban house, the team work to identify the bodies buried in the garden. Meanwhile, Jack must choose between his brother and the truth.

Nikki, Jack and Adam investigate the murder of a surgeon in a hospital. DNA evidence appears to implicate a patient who was under anaesthetic at the time of the killing.

The murder of a promising boxer draws Nikki and Jack into the world of underground boxing. Meanwhile, Jack's brother Ryan is released from prison.

Jack, Nikki and Simone investigate another death connected to the underground boxing ring. Jack's loyalty is tested when he fears Ryan has put Cara in danger.

Nikki’s students make an alarming discovery while dissecting a body donated for their training. Jack and Simone try to save care home residents from a flood.

Stranded in the flooded care home, Jack and Simone fight to keep the residents alive - but Nikki discovers that they may be trapped inside with the killer.