It's Fiona's birthday, and she's not going to forget it! While inspecting a possible Islamic terrorist safe house, they are kidnapped. With the threat of his son's, his wife's and Danny's life, Adam must choose who won't live to see another day, Fiona or Danny? The prime minister's life is in danger. Will MI5 give into the kidnappers demands? But then to everybody's surprise... Danny makes the ultimate sacrifice.

When a devastating bomb explodes in central London, causing multiple deaths, 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.

Far-right political party The British Way is threatening democracy so Adam and Fiona go undercover to infiltrate and destroy its campaign.

The Syrian foreign minister tries to establish subversive contacts with MI5 at the opening of a cultural centre in London. Fiona is desperate to lead this mission and must confront her Syrian past.

An old British traitor is called in to infiltrate a Russian firm suspected of stealing secrets from GCHQ.

Harry upsets the CIA by stopping an extradition to the USA.

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.

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 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.

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.

The team steps in when a British soldier is kidnapped by Al-Qaeda. Meanwhile, an old protégé of Harry's returns to the fold after eight years in a Russian prison - but whose side is he really on?