Adam and Ros recover to find London facing an even greater threat. While attempting to thwart an attack that could jeopardise a historic peace accord between Britain and Iran, the team unwittingly unleash a deadly killer. But with a virus that mimics the pneumonic plague, there can be no negotiation. And when Zaf is kidnapped by armed mercenaries, the team realises that in a game of the highest stakes they hold none of the cards. As the stuff of nightmares becomes increasingly real, London faces total devastation.
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.
A British plane is thought to have been hijacked and taken to an American airstrip. Ros is captured by the Yalta organisation when the team show up and they learn of an international cover-up.
As an Algerian extremist escapes his home detention, the team fear he may be plotting a terror attack on US businesses in the UK with the help of local Iranians. However, working with the Americans to stop the attack proves a trying task given their recently-deceitful behaviour.
MI5 have to intercept a Russian arms dealer who plans to pass blueprints for a nuclear device to Iran. Adam and Ana decide to bring their relationship to a close.
Harry discovers there's a mole at large in the Grid. Meanwhile, Ros and Adam board a plane undercover in an attempt to stop Iran becoming a nuclear power.
A live TV broadcast announcing the new peace accord between the UK, US and Iran is hijacked by armed gunmen. Can Adam and Ros defuse the situation before someone's hurt?
Ros is in grave danger after Bob Hogan discovers she's a traitor. Meanwhile, Harry's brought before Yalta's chief, whose identity shocks him to the core.
The team find 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 realise that if they respond their lives will be in danger but if they don't it will be public who suffer. A shocking discovery is made when they discover who is behind the