Episode One

The series begins with a very literal bang, when young MI5 agents Tom Quinn, Zoe Reynolds and Danny Hunter investigate a car bombing which has claimed the lives of a family planning doctor and her daughter. But this is only the blood-streaked tip of an ominous iceberg, as 19 other bombs are known to have been smuggled into England. The suspected orchestrator is American pro-life zealot Mary Kane, who already faces the death sentence in Florida for an earlier bombing. Zoe Reynolds must now go undercover in Mary Kane's extremist organisation to discover the whereabouts of the other bombs – but it's not going to be easy, not least because the CIA is determined to grab Mary quickly, no matter what...

Episode Two

Shocking twists and a brutal adversary make this one of the most memorable Spooks episodes of them all. At its centre is Robert Osborne, the bigoted and manipulative instigator of violent race riots across the country. He also happens to be extremely savvy when it comes to security and surveillance, so MI5 decides to send Tom and Zoe undercover as husband and wife to get close to Osborne and find out what he's planning. But in the last moment Zoe is called away on another assignment, to be replaced by the keen but inexperienced Helen Flynn. Will she find herself in over her head on this extremely dangerous mission? (Yes, she will).

Episode Three

Facing the business end of a gun is all in a day's work for the spooks, as Zoe discovers in Episode Three. While attending a function at the Turkish consulate, she and many others suddenly find themselves in the middle of a hostage situation when the building is stormed by Kurdish freedom fighters led by the ravishing Leyla Ahmed. Their stated aim is to secure the release of their fellow rebels in Turkey, and it's down to Tom and Danny to orchestrate a surveillance operation at the consulate. But things aren't quite what they appear, and it soon transpires that there's a shadowy figure behind the siege – a man with disturbing ties to the spooks themselves...

Episode Four

Anti-globalisation rallies may not seem to constitute a major national security risk, but the spooks are taking no chances and dispatch Danny and Zoe to observe a huge protest in London. On arriving at the scene, they're stunned to see legendary MI5 agent Peter Salter undercover among the protestors. It seems he's on a secret operation of his own: to track down the militant anarchist Istvan Vogel. But is Salter in too deep for his own good? Just whose side is he on? As the spooks try to discover where Salter's loyalties lie, Zoe must also come to terms with startling revelations about Tessa Phillips, the MI5 mentor she has idolised for so long.

Episode Five

Absolute power corrupts absolutely – and the truth of that saying is made very clear in Episode Five when the spooks find themselves dealing with Hampton Wilder. A disgraced politician who has recently served time for embezzlement, Wilder tells MI5 that, while in prison, he wrote a memoir implicating a top MP as an illegal arms trader. Having found God, Wilder then decided to destroy the manuscript – only to find it had gone missing. The MP in question is the Prime Minister's closest friend, so if the press get wind of the story, the ensuing scandal could very possibly destroy the government. But who has the manuscript now? And just what role does MI6 have to play in all of this?

Episode Six

The question of negotiating with terrorists is a thorny one. Should it ever be done? The spooks face this deadly dilemma in the final episode of series one, when they're approached by Patrick McCann, leader of an Irish splinter group who claims that Middle Eastern terrorists are planning an attack on a British nuclear power plant. McCann says he will share all the details with MI5 on the condition that they call off surveillance on McCann's paramilitary organisation for 30 hours. The proposal triggers in-fighting among the team, with some believing that he's about to unleash his own terrorist outrage in England. But with the threat of a nuclear explosion looming large, the spooks may be forced to give in to his demand.