Jake Armstrong believes Becky Rackley is the recipient of his wife's donated heart. She thinks the same, but neither tells the other. She's a spy, working for MI5. He's an insurance investigator, specialising in the theft of valuable works of art. When a terrorist organisation threaten to blow up London with a dirty nuclear bomb and Jake tells Becky he's going to Moscow to hunt for a stolen painting, she wires him up-without his permission-to keep track of his movements. The plan goes wrong; the clock starts to tick, and London's evacuated. Becky flies to Moscow in a desperate attempt to avert a world catastrophe and find Jake, dead or alive.