A car bomb explodes in Liverpool and Zoe is sent undercover to investigate. Tom's life gets complicated when he falls in love with a woman he met while working undercover.

The team uncover connections between racist ring-leaders, politicians and mass killings of immigrants, and are forced to go undercover in order to investigate.

Zoe is caught in the middle of a siege on the Turkish embassy, while Tessa is stunned and confused when she sees a man from her past.

Ellie questions whether she can cope with dating a spy, and Zoe discovers Tessa is up to something. Meanwhile, Tom's mentor is working undercover at an anti-Bush rally when his methods start to appear dangerously unconventional.

Disgraced MP Hampton Wilder's memoirs could create a scandal big enough to bring down the government.

Patrick McCann, the leader of an Irish splinter group, walks into a safe house armed with a grenade, and demands to speak to someone at MI5 about some crucial information he has on a Middle-Eastern terrorist group called Asabiyah.