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.

When Florence Clarke confesses to the murder of her husband, the investigating detective reveals a startling connection to a painful secret for Simone.

Jack's father sends him on an urgent mission into the mysteries of his past. Meanwhile, Nikki and Simone investigate a body that seems to hold puzzles of its own.

The death of an investigative journalist throws the spotlight onto 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.