Berlin. 1963. The height of the Cold War. An early morning spy swap, not at the familiar setting for such exchanges, or at Checkpoint Charlie, where international visitors cross into the East, but at a more discreet border crossing, usually reserved for East German VIPs. The Communists are trading two American students caught helping people to escape over the wall and an aging MI6 operative. On the other side of the trade: Martin Keller, a physicist who once made headlines, but who then disappeared into the English prison system. Keller's most critical possession: his American passport. Keller's most ardent desire: to see his ex-wife Sabine and their young son. The exchange is made with the formality characteristic of these swaps. But Martin has other questions: who asked for him? Who negotiated the deal? The KGB? He has worked for the service long enough to know that nothing happens by chance. They want him for something.