When a devastating bomb explodes in central London, causing multiple passings, a terrorist group with a hatred for human life claim responsibility. With their leader facing extradition, the bombers announce that crippling attacks will be launched at ten hour intervals until he is released. Will the team be able to track down the perpetrators before they strike again?

Zafar and Adam race against the clock to uncover the latest bomb. As a new ultimatum is issued and Tash mysteriously disapears, the team is forced to deal with the possibility of a mole within their own organisation.

MP William Sampson sparks civil unrest and racist attacks in his constituency when he defects to the far right-wing british way party. With more MP's set to follow the lead of Sampson, Harrys team are told to discredit him before democracy is threatened. Helped by Ruth, Adam infiltrates the BWP and engineers a rift between Sampson and his deputy Keith Moran. Fiona pretends to be a PR supremo and makes Sampson a laughing stock in front of the media. With the BWP finished, Sampson and Moran learn of Adam's role in their downfall and soon Fiona and Ruth are in a battle to survive

Adam has his hands full trying to turn a prominent terrorist into a double agent in order to avert another major bombing in London. Adam has to go undercover and join illegal immigrants being transported to the UK from Turkey. Among them is Ali Muhammand Yazdi, the founder of an al-Qaeda splinter group.
The operation appears to have been funded by a Middle Eastern prince who, informant Yazdi says, is a key London terrorist cell member. MI5 takes the prince into custody, but can Yazdi be trusted?

The agents are assigned to protect a journalist who is about to break the story of a former Cabinet Minister with a shady past. But the task gets complicated when it is revealed that the minister was cuddled by a neo-conservative group with connections to the government.

When MI5 get information that a suspect is coordinating an attack from prison, they make a decision to release him. Will he lead them to a terrorist network?

Adam and Fiona's marriage is tested to the breaking point. Against Adam's wishes, Fiona insists on going under cover in an operation which leads straight back to her troubled past with devastating consequences.

The agents are forced to rely on a well-known traitor as they infiltrate a Russian company.

Harry Pierce prevents the illegal extradition of a suspected terrorist to the U.S. and, determining that the suspect poses no threat, releases him. The terrorist laterhugs the MI5 officers surveilling him, and Juliet has no choice but to relieve Harry of his duties.

A former spook with a secret agenda holds the team hostage, threatening to blow up Thames House unless they tell her the "truth" about the passing of Diana, Pricess of Wales. Ruth is left to try to talk her out of her cuddleous plans, but the team fails to see their former colleague's real agenda until it is too late