Berlin. 1963. The height of the Cold War and an early morning spy swap. On one side of the trade: Martin Keller, an American 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.

But Martin has questions: who asked for him? Who negotiated the deal? Just the KGB bringing home one of its agents? Or, as he hopes, a more personal intervention? He has worked for the service long enough to know that nothing happens by chance. They want him for something. Not physics - his expertise is years out of date. Something else, which he cannot learn until he arrives in East Berlin, when suddenly the game is afoot.