Nikki struggles to come to terms with life back home and seeks out fellow pathologist Sally Vaughan for support, only to learn she is nowhere to be found. National Crime Agency investigator Guy Bernhardt asks Nikki to help him by employing pathologist David Cannon, the chief suspect in Sally's disappearance. As Jack, Clarissa and Thomas share concerns about Nikki's wellbeing, a body found in a reservoir is linked to a murder case from 16 years previously. Return of the crime drama, starring Emilia Fox, with Julian Rhind-Tutt and Alex Macqueen.

Nikki's suspicions about David Cannon are roused further when she discovers blood in the boot of his car an with Thomas's support she takes samples to process. Does it belong to Sally Vaughn? Meanwhile, the uncovering of the body from the 16-year-old murder shines the spotlight on three people who went to the same school. Emilia Fox stars, with Julian Rhind-Tutt and Alex Macqueen.

A woman is murdered and the forensic evidence takes the team to a cosmetic clinic where the victim had been receiving various treatments seemingly for free, but Nikki and Silva are frustrated by the CEO of Hamilton Ashe hospital when he blocks access to Karen's medical records. Meanwhile, when his daughter Rosie turns up at the Lyell as her mum is in hospital over a pregnancy complication, Thomas must play the doting father for a few weeks - a role that does not come naturally.

Nikki comes face-to-face with Simon Laing once again as the motive for the murders appears to be blackmail. The hospital computer database has been hacked and Clarissa and Max follow the forensic clues to a teenage hacker called Splinter. The danger comes much closer to home, however, when Nikki receives a threatening text with a picture of Rosie.

A US diplomat is shot dead in central London, forcing the team to work closely with the embassy and the FBI.

Nikki is still in shock as the team arrive at Matt's residence but insists on working at the Lyell, determined to help. When analysing crime scene photos and the positions of the victims' bodies, Nikki realises there is a pattern. Together, the team uncover a secret that has been held by those at the very top of the US government.

While two care home staff are chasing Kevin McDowd, a young man with learning disabilities and sociopathic tendencies, Nikki and Jack examine a fatal road accident where the deceased is Kevin McDowd's mother. The investigation led by police sergeant Button should be straightforward, but the forensic evidence suggests foul play.

The team are determined to uncover the truth about unexplained deaths of patients at a care home. They are desperate to rescue Serena and return her to safety. Unbeknownst to her colleagues in the Lyell Centre, Clarissa allows herself to be admitted to the care home in order to investigate. Her determination to find out what happened at the care home leads her to uncover a shocking truth, but puts her life in danger.

It is Christmas morning and Nikki is awaiting a call from Matt who is back in the States. Instead, she receives a call to say that the team is needed: a family has been massacred at an enormous property owned by Andy McMorris, the CEO of a haulage company. Greeted by SIO DI Gibbs, Nikki is first on the scene whilst Clarissa is connected to the action via screens and microphones back at the Lyell. Having left his father to celebrate Christmas without him, Jack is just arriving to join them when a gunshot suddenly rings out. With Gibbs lying on the floor with a life-threatening injury, the team realise that the shooter might still be on the grounds. Are they also in danger?

As the truth behind the McMorris family is revealed, the team is brought together by the conclusion of a shocking Christmas family tragedy. Reuniting with their respective families, Nikki finds her secret Santa gift is a visit from a loved one.