Charlie Green's first mission with Field Office 19 is to foil an apparent assassination plot against the British prime minister. Charlie finds himself in uncharted territory when he unwittingly becomes team leader and is given five and half hours to track down the would-be killer.
Protestors hack into Emergency Communications System and broadcast a video of dead inmates at a government prison. MI5 publicly deny the footage is real, prompting the terrorists to set off a series of false alerts. Jez realises he's partly responsible for the chaos but does he have the power to stop the extremists before it is too late? Charlie discovers MI5 corruption directly relating to the London bombing.
Jez and Kylie are sent in undercover to investigate a housing estate which has become a criminal hot-spot and source of fake radiation drugs. The killing of a police officer on the estate complicates matters, putting the pair in grave danger. Charlie and Rachel discover further clues in the investigation of Hannah's death and MI5 corruption.
The horrific murder of two MI5 informants lead the team to discover a leak at a government-run Missing Person's Scheme. The race is on to find the source of the corruption and stop the killings before they escalate. Rachel goes undercover to find further information on the MI5 cover up and learns a British scientist may have been wrongly imprisoned for his part in the bomb plot.
A bank heist by eco terrorists, involving a 16-year-old suicide bomber, leads the team to uncover a secret deal between the British government and a Korean billionaire. Will the team be able to free the hostages and stop the terrorists from completing their deadly mission?
Charlie speaks to the British scientist wrongly imprisoned for the London attack and discovers there may be a second nuclear bomb.
With the anniversary of the London attack imminent and the knowledge there may be a second nuclear device still out there, Charlie and the team have 24 hours to locate the bomb and identify the MI5 traitor before another major national catastrophe is allowed to happen.