"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 a lower level CIA operative. On the other side of the trade: Martin Keller, a physicist...