Nikki arrives at a murder scene to find it's a carbon copy of a case in her past.

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.

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.