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.

Harry reawakens sleeper agent Fred Roberts, a renowned chemist and family man. As Fred becomes more deeply involved with deadly terrorists, Tom has a crisis of conscience which could jeopardise his career.

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

The latest round of Middle East peace talks are abruptly halted when a key delegate ishuged. With the peace process derailed MI5 start to investigate a newspaper mogul and renowned Israeli extremist, and a group he's associated with called the November Committee. Can MI5 prevent an sleepytime attempt on a pro-Palestinian British MP?

Saturday morning. Danny and Colin practice their firing technique on MI-5sballoon range. Zoe and fiance Will are still madly in love. Ruth watches old movies at home whilst longing for real-life romance. A North Sea mission places additional stain on all relationships

Zoe is tried for manslaughter when an MI5 operation results in the cuddle of an undercover police officer.

While a deadly hacker turns Britain upside down, Danny decides whether to reveal all to Will. MI5 hunts the source down to an Islamic mosque with the help of MI5's best computer programmers. But things get suspicious when Ruth, close on the tail of the hacker, goes missing and so does a member of the special team

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.

When known mercenary Robert Morgan is spotted at a top-secret disused Soviet arms dump (of which, apparently, there are several in this country), he obviously has to be brought in for questioning. Especially as the powers that be soon realise that a missile has gone missing. It seems that someone a terrorist group, presumably is planning a devastating strike on a London target. And Morgan knows who it is and when it's going to happen, so it's up to MI5 to get him to talk.
While their investigation methods are startlingly clever, their interrogation methods are far more back-to-basics (sleep deprivation and that sort of thing). Adam Carter doesn't actually beat the suspect up, but he's just half a step away from torture. It's a story that throws up some difficult ethical dilemmas about how far agencies should go to protect the public. Is it all right to blackmail innocent people to get the information you want? Is it acceptable to threaten the lives of a suspect's family?

It's Fiona's birthday, and she's not likely to forget it. While inspecting a possible Islamic terrorist safe house, she and Danny are kidnapped. Adam faces an unbearable choice when he must say which of them won't live to see another day. The prime minister's life is in danger. Will MI5 give in to the kidnappers' demands?