Adam and Zaf target a UK-bound terrorist with a train bomb in Tehran. As the operation goes catastrophically wrong, the team learn of the darker goals of theirmission and the influence of a mysterious external agent, with the repercussions of the Tehran blast felt on the streets of London.

As the team fear reprisals against Iran following the revelation of their bio-weapons programme, a British plane is apparently hijacked and flown into a US air base. But after they visit the base and Ros iscaptured by the shadowy Yalta organisation, they discover the sordid extent of an international cover-up.