The Berlin Exchange Mysterious Book Report No. 486 by John Dwaine McKenna What happens to a traitorous American, a scientist who spied for the Soviet Union and gave up our atomic bomb secrets, when he’s released after ten years in a British prison in the U.K., swapped for a busload of political prisoners and sent to East Germany?  That’s the opening premise of The Berlin Exchange, (Scribner, $28.00, 320