I-5 has Sergei Valentino, a freelance Russian, under observation from the moment he enters Britain. He has in his possession blueprints for a nuclear trigger which they believe are destined for the Iranians who seem bent on developing a nuclear weapon. Soon after his arrival they lose him however and Ros uses her Yalta connections to find out where he is. Yalta expects something in return, however. Adam meanwhile has his own problems after he accidentally kills a mugger who turns out to be a journalist who was investigating the Tehran bombing. Adam has been hiding Ana Bakshi in an MI-5 safe house without permission and Harry Pierce thinks she might be leaking information. He's definitely been set up, but the source lies elsewhere.

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