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.

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.

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.

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 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.

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.

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.

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

Jack's world has been blown apart following the discovery of Hannah's dead body. Nikki manages to find out the truth behind Jack and Ryan's strained relationship. Thomas thinks about hiring forensic scientist Helen as Jack's permanent replacement. Christy Nash is scared for the future of his marriage and business after DI Carter finds out abouts of his relationship with 15-year-old Katie.

Fresh from her trip to the States, Nikki and the Lyell unit are called in to investigate an attack against a trans man. When two further attacks are reported, one leaving a potential witness, it becomes clear that the team is facing an outbreak of violence against the trans community.

A woman's body is found on railway tracks in London. When the post-mortem reveals signs of domestic violence, it brings back troubling memories for Nikki.

When the team's search for Jenny's killer hits a wall, her friends at the women's refuge seek answers. Meanwhile, Thomas makes some friends in high places.

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 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 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 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.

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.

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.

The police grow frustrated with the lack of a forensic link, but Sam finds more clues in an old case.

The revelation that Flannery's first wife also died of a stair fall sends Harry to Prague to seek evidence to prove the man's guilt. However, Nikki's determination to look beyond the police's blinkered investigation leads to further tragedy.

After the body of a pregnant Northern Irish girl is found, Nikki and Jack need to locate the baby that has been snatched from her womb. Thomas discovers the girl’s connections to a criminal underworld.

A woman's body found floating in the Thames leads Nikki and Jack to a community on the banks of the River Lee. Three years ago a teenager called Ruth Tresize went missing from the area, leaving the locals haunted by suspicion and grief. A fresh spate of killings reopens these old wounds.

Nikki is under fire for leaking information on a suspect, and Thomas is called in to play peacemaker. Jack and DI Ashton track down the mystery witness. Before the killer strikes again, the team must uncover the true story of Ruth Tresize's disappearance three years earlier.

When Mark James's decomposing body is discovered, it bears all the signs of a ritualistic killing.