Nikki and Jack strive to track down a sniper at large in London and stem a public crisis.

Nikki and Jack investigate links between the victims to close the net on the killer.

Nikki and Jack investigate a man killed by a train on the London underground.

Nikki helps high-flying DI Luke Nelson unearth painful childhood memories.

A suspected paedophile is found murdered in a children's playground.

Nikki, Jack and Thomas focus in on Lizzie's movements on the night of Barge's murder.

The nanny of a Russian oligarch is killed in a botched assassination attempt.

A young woman working for the Doshis is found dead in Maksim's apartment.

The Lyell team are under pressure to catch the killer of an admired Essex police officer.