Nikki becomes the prime suspect after a former colleague is murdered.

A young British Muslim returns to the UK, and concerns over her intentions soon escalate.

Thomas must put his personal feelings aside as the team track down Begovic.

An ex-convict is killed and suspicion lands on a recently released child killer.

Further victims are killed and a distinctive modus operandi begins to become clear.

The shooting of a teenager in an armed police operation triggers a series of murders.

Jack leads the hunt for suspected killer Bruno, the brother of the shot teenager.

A family murdered at a picnic leads the team to the female victim's estranged husband.

As Nikki and Jack move closer to the truth, their lives are thrown into mortal danger.