A plague-like virus is unleashed in London. Facing the prospect of half a million dead, Harry orders the team to take extreme measures in an attempt to obtain the antidote from allies who may be keeping it a secret.
The team investigates a suspicious plane crash near an American airbase in the UK and uncover a link to the mysterious "Copenhagen". Ros's captors subject her to mental torture and reveal some disturbing news about Zaf.
Abdul Kharami is a suspected terrorist who is under constant surveillance but manages to evade his watchers just as MI-5 receives reliable information that he may be ready to stage an attack. Kharami specializes US targets and given the Americans set them up with the Tehran explosion, Ros for one thinks they should just ignore him. Harry Pearce thinks otherwise and brings his American counterpart, Bob Hogan, up to date. He also authorizes the launch of Operation Zebra, MI-5's plan to infiltrate the CIA. When Kharami's plan is traced to the Iranian Special Consul, Adam...
On his way to intercept a Russian arms dealer planning to sell nuclear weapons blueprints to Iran, Adam, in self defense, kills a mugger who later turns out to be a journalist. Adam has a last fateful encounter with Ana.
Adam and Ros board an airplane to identify a courier carrying nuclear weapons technology to Iran. Jo and Malcolm race to prevent the poisoning of London's water supply which Iran has threatened if the courier does not reach his destination.
Aware that Iran now has full nuclear capability, Harry and Bob convince Bakhshi go on live television to announce that Iran has ended its uranium enrichment program, but armed activists learn the truth and hijack the broadcast.
War with Iran finally averted, the team learn that a London school will be the target of hardliners resisting the new peace. Simultaneously they discover that their lost colleague, Zaf, was grotesquely tortured and killed by a group of mercenaries. When Jo is snatched by the group, Adam resists calls to stay focused on the school threat; the war has become personal and he must find Jo at all costs.