As they get to the heart of their investigation, the Lyell team navigate corruption, loss and deceit within the local police force, who have become a law unto themselves.

Jack comes to the aid of an old friend, and is sucked into a difficult case, where he is pitted against his former mentor. As Nikki and the team start to create a picture of what happened, they learn nothing is as it seems. Dealing with a family of serving police officers, they have to tread carefully, as their relationships prove to be another obstacle for the team to overcome.

Levelling-up leaders and environmental activists clash in a small town trying to look to the future. With a sabotaged train and a dead mayor, the activists become suspects.

A lorry is found with people locked inside, some dead. With the survivors refusing to speak, Nikki and the team must use their pathological and forensic skills to identify them.

The Lyell team are thrown into the dark side of social media, where nothing is as it seems, and the perfect profiles of the influencers they are investigating raise disturbing questions. As a heavily pregnant DI asks the team for their expertise, are they running out of time to solve this case?

The Lyell team return to the tunnel and uncover some difficult truths, while the police raid the protester camp, desperate for answers. Family ties are pushed to their limits.

The Lyell team work together to find out why the lorry was found with bodies inside and a dead driver at the wheel, and are truly shocked to discover where it leads them. Gabriel becomes emotionally invested and is presented with an ethical dilemma, and Jack gets a surprise visit.

When a man plummets from a high-rise building, the Lyell team cross paths with the NCA and a notorious mafia group, pushing Nikki to make a tough decision.

The investigation continues to take unexpected turns, with Nikki managing to get behind the mask of the lead suspect. Jack has a breakthrough at the festival site and Nikki takes a dangerous opportunity. A surprise event at the Lyell brings some hope.

Nikki becomes even more involved with the Ndrangheta mafia-group and Jack uncovers some disturbing leads. An unlikely alliance leads Nikki closer to the truth, but not without some collateral damage.