In 1962, the American sighting of a new missile base in Cuba during a regular air rescue sparks fears that the Soviets are going to establish a military presence there. In response, a 'quarantine zone' - in reality a naval blockade - is set up around Cuba, preventing Soviet ships from importing their nuclear hardware.Meanwhile, the death of a double-agent is causing ripples within the British Secret Service. SIS Chief Charles Winter investigates, only to discover that the double-agent's KGB control, Vasili Korznikov, has recently defected to American Intelligence. Washington isn't keen to let Winter investigate Korznikov, and he soon discovers that neither frauds nor turncoats can be trusted. But there's little time for diplomacy, since the Russian ships are already on their way to Cuba...