MI5 investigates the assassination of a Muslim cleric outside the high court, and uncovers a radicalised Christian who is determined to incite a religious war.

MI5 is put in charge of protecting Niko Grecic, the former right-hand of Tezlia, a Serbian who is put on trial for war crimes. They know that Richard Dempsey, a former MI6 agent who turned on them, is looking for Grecic to kill him before he can testify. Adam, Jo and Zafar must protect Grecic at all costs.

An environmental terrorist group is threatening to flood London if the government does not make a secret document public.

Zaf goes deep undercover to infiltrate an Al-Qaeda cell that is planning an attack on the UK. When Adam learns that the terrorists are on a suicide mission he tries to prevent them from reaching their target, but events soon spiral out of control.

The government publishes its report on the investigation into the death of seven terrorist suspects in a fire at a prison. Harry suspects a cover-up, then discovers that one of his team has been implicated.

Adam and Zaf try to find a group of terrorists who have infiltrated Britain. Ros oversees a visit by a delegation of Saudi princes offering a guaranteed oil supply in exchange for nuclear expertise, but the Saudi Trade Centre is attacked by terrorists.

The terrorists start to execute hostages in pursuit of their demand for the release of Al-Qaeda prisoners held in Saudi Arabia, but suspicion arises as to the true identity of the terrorists.

MI5 has foiled an attempt to murder the Home Secretary, but the plotters use the new emergency powers to imprison Harry. The team must try to frustrate the coup before Harry is executed.

Posted undercover at the World Trade Summit for Africa, the team discovers an assassination plot. Initially determined to put their lives on the line to prevent the murder, they are faced with a moral dilemma on discovering the motive behind the plot.

The government introduces Draconian emergency measures in response to a series of terrorist attacks. MI5 fears that influential establishment figures are behind the attacks and may be planning a coup.