In October 1990 West German general Jorg Schonbohm and a small team of experts moved into the headquarters of the former East German army to effect the unprecedented: the takeover, in peacetime and without the firing of a single shot, of a well-equiped army that had been the Bundeswehr's main enemy only a few months earlier. What Schonbohm discovered and recorded in a diary was almost incredible: plans to conquer West Germany's major cities; blueprints for a surprise attack on West Berlin through the city's subways and sewer systems; papers documenting the planned use of chemical weapons. But...