Tom Quinn has disappeared after shooting his boss Harry Pearce. He also stands accused of assassinating the Chief of Defence Staff. Chairman of the Joint Intelligence Committee Oliver Mace uses this a pretext to launch a punitive investigation of MI5. Zoe, Danny and the team must prove Tom innocent and save the service from government takeover.

Danny and the team must uncover the truth behind an assassination attempt on a famous novelist.

The baby of a celebrity couple is kidnapped and they call in MI5. Fiona goes in undercover to gather more information about the couple against Adam's wishes.

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.