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.

With their suspect in a coma and an attacker seemingly at large in the hospital, Nikki calls on Adam’s expertise to help solve the case.

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.

Sam Ryan recruits the Lyell team to investigate the assassination of the health secretary, but Nikki is unsure whether Sam knows more than she's letting on.

DNA evidence linked to the health secretary’s assassination forces Nikki to face her past in the present. As her investigation progresses, Nikki realises that its consequences will affect her, and her profession, forever.

When a woman confesses to murdering her husband, the Lyell team must determine if all is as it seems. Meanwhile, Simone is shocked to be reunited with a detective from her childhood and struggles to untangle her past.

A secret from his father propels Jack to Belfast. Meanwhile, Simone and Nikki investigate the mystery of a burned body. As familial secrets come to the surface, Jack faces tragedy head on.

The death of an investigative journalist throws the spotlight on to Sam Ryan. Nikki begins to realise that the implications of her discoveries will challenge the principles of forensic science.

Events lead Nikki to conclude that getting the truth will put the Lyell team and everything they love in danger.