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.

Zaf and Adam participate in a mission in Tehran that goes wrong. As the investigation advances, the team realizes they've been lied to as to the goals of their mission.

The country faces a plague outbreak. In a race against time, the officers from Section D have to track down and quarantine everyone who might be infected, while preventing a panic.

The team finds themselves suspended from the Grid following what happened involving Ros. Harry learns from an old adversary about a bomb he has planted in London. The team realizes that if they respond their lives will be in danger but if they don't it will be the public who suffers. A shocking discovery is made when they discover who is behind the latest threat.

With Lucas back within MI5 he reveals that the Russians interrogated him about Operation Sugar Horse, the most secret ongoing spy operation MI5 ever had. If the Russians know about it, then MI5 has a very high level mole. Harry seeks out his mentor, The Spycatcher, to help him find the mole. Ben is undercover with an Al-Qaeda cell; they are planning to bomb London and what looks like a dry run unexpectedly turns live.

The team is stunned to discover that Al-Qaeda's number three wants to negotiate. It's a risk, but Harry and the team have to take this chance for peace.

Harry is imprisoned and accused by MI5 of being the Russian mole. Lucas disappears to Moscow in a bid to gather intelligence and get to the bottom of Harry's arrest, whilst the rest of the team tries to prove his innocence on the Grid. But with so much evidence against him and a traitor among the team, things aren't looking good for Harry.

With the Russians launching a nuclear strike on London, the only person who can help the team in this desperate hour is the traitor amongst them. With the Russians hunting them down, the team ushers their traitor through London in a desperate bid to reach the codes, and the bomb, in time.

Harry is still missing, and there is one question on everyone's mind: is he dead, or alive?

Section D discovers that Harry thwarted a clandestine operation to smuggle weapons-grade uranium into Iraq to justify the war. Now the rogue officers who masterminded the operation want their uranium back, and they are prepared to go to any lengths to get it.

If Harry isn't dead already, is it too late to save him?

The country reaches crisis point when energy supplies are threatened by an explosion at a gas processing plant. With reserves on the verge of running out, Britain is forced to turn to Tazbekstan for help.

But in return for energy, the Tazbek Trade and Industry Secretary, Urazov, wants carte blanche to wipe out his enemies on British soil. Is this a price worth paying or can Section D get rid of Urazov in order to secure the deal?

The pressure is on for Section D when a secret meeting of powerful tycoons is stormed by armed terrorists and eight of the world's richest men are taken captive.

But this is no normal hostage situation - undercover at the time, Ros is one the hostages. As events spiral out of control, it looks like no one will make it out alive. Is this the end of the road for Ros?

Harry is puzzled by the sudden death of CIA boss Samuel Walker. Harry is convinced that he did not commit suicide and when another CIA agent dies he begins to think that the deaths have something to do with the power meeting that is being held in Basel. Ros is surprised when her old mentor, Jack Coleville, contacts her and it soon becomes apparent he is involved in what has been going on.

With the country on the verge of bankruptcy, the government can't pay its national debt payments. Section D is asked to get back more than a billion pounds of illegal earnings from the DeWits Bank. The team has to find out what, or who, Nightingale is after Ruth's investigations into the power meeting at Basel pay off.