Nikki arrives at a murder scene to find it's a carbon copy of a case in her past. She soon fears the killings are personal to her.

Nikki becomes the prime suspect after a former colleague is murdered. Jack, Thomas and Clarissa fight to clear her name.

A young British Muslim returns secretly to the UK, initially suspected of drug smuggling, but soon something much more sinister is feared.

Thomas must put his personal feelings aside as the team track down Begovic before she and her extremist compatriots strike out again. It soon becomes clear that Begovic isn't working alone and may not have been the one who shot Ryman. In fact, her accomplice may be a man previously assumed dead.

When an ex-convict is brutally murdered, the Lyell team is introduced to a forensic psychologist who works closely with those released from prison on life licence.

After the team discovers that suspect Paul may not be who he says he is, the investigation revisits an infamous murder case from the past which he was involved in.

The fatal shooting of a teenager in an armed police operation triggers a series of murders that link gangsters, a grieving family and a fractured firearms unit.

Jack leads the hunt for suspected killer Bruno, the brother of the Polish teenager shot by the armed police, and enters London's small but devastating gun trade.

A family murdered at a picnic leads the team to the female victim's estranged husband. But all is not what it seems, and Nikki and Jack are thrown into mortal danger.

Nikki and Jack are thrown into mortal danger as they uncover a high-powered world of sex and depravity. Meanwhile, Amy confronts her past.