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. With the Lyell under increasing financial scrutiny and frustration growing between the team and the acting DCI, can they pull it together to find the killer before they strike again?

A slip-up from DCI Cramer results in the premature release of a suspect - and when his mistake becomes evident in the light of incriminating evidence, he tries to blame the Lyell for the oversight. With the team under increasing scrutiny, Thomas offers to bear the brunt of the pressure while the team focus on the search for the perpetrator. When his career in the field is threatened, will Thomas leave the Lyell to save his team?

After a teenage boy dies in a meth lab explosion, his inspirational head-teacher Noah Taylor resolves to confront the drug dealers praying on his community. Dangerous batches of new drugs are hitting the streets and it's down to Nikki, Jack, Clarissa and Thomas to deal with the consequent rise in overdoses.

When tragedy strikes at the heart of the Taylor family, it puts Noah on a collision course with the criminals behind the drugs. Meanwhile, one of the team's life is endangered when they become the victim of a knife attack.

A collection of dismembered body parts, covered in intricate Japanese tattoos, has been found in a Brighton waste dump. The team is called in to piece them together, painstakingly searching for clues that could lead them to the killer. Outside of the lab, Nikki has some news that she desperately wants to share with Matt.

The team struggle to find the final piece of the puzzle left behind by the murders in Brighton. At home, Nikki and Matt discuss their future together.