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.

Rising star Sergeant Sam Honeywell is found beaten and shot in his burnt-out car in Essex. The police are up in arms in what is a hugely emotive and political case for them, and DCI Jim Sullivan is determined to nail Honeywell's killer. When a local drug dealer and son of known crime boss Dean Fallon seems to have his alibi sewn up, suspicion shifts closer to home. Honeywell is discovered to have been in an affair with Kate Parry, wife of his best...

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

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 and the ominous message - 'lose the evidence'.

Tension on the tube network threatens to boil over, and security is stepped up. The accidental verdict in the first death is called into question and the witnesses are brought in for interview. Amongst them is Lana Sutherland, a young hotel worker who has taken in a homeless man, Owen. DI Nelson lets Lana slip through the net before he realizes she may be harboring a dangerous killer. Nikki helps Nelson unearth the mystery of his father's death, allowing...

Nikki reaches out to Becky to help her deal with her trauma, as her father is implicated in the killings. Jack's paranoia about Clarissa leaving deepens further when the pair joins forces with Max. And the death of a schoolteacher proves key to the mystery.

Known Essex criminal Jason Simons is found murdered in a way that is perhaps too similar to Honeywell to be a coincidence. As anomalies in his post-mortem stack up, the team discovers that Simons was not what he seemed. Traces of drugs on Simons' penknife point them towards a major drugs importation, but his bereaved girlfriend Tess claims to know nothing about it. Suspicion turns back to Dean Fallon, but a discovery in his medical records and the...

Diplomat Ryan Reed is watching the US ambassador on a late night current affairs show. However, when heading home he is seemingly targeted by an assassin. Led by SIO DCI Ben Solomon, the Lyell team arrive at the scene to find Reed's body posed - sitting upright on a bench with his hand tucked inside his jacket. An argument ensues between the Police and the US Embassy staff who claim the murder falls under their jurisdiction. Our team have to fight...

Having found a link between the two cases, the team struggle to make sense of it. Nikki visits a disgraced former colleague who may hold the key. Thomas uncovers the bizarre truth about how Tina died.

Nikki, Jack and DS Ross find themselves under pressure to urgently close the net on a serial killer abducting young women. Concerns grow over missing Sarah, and solving her mysterious disappearance becomes an urgent priority for Nikki and Jack. Nikki's confidence in the detectives is diminished when she suspects a cover-up in the past case of a murdered prostitute and her pimp.