The Tristan Betrayal by Robert Ludlum
1940: the Nazis are at the height of their power. France is occupied, Britain is enduring the Blitz and under threat of invasion, America is neutral and Russia has an uneasy alliance with Germany. American Stephen Metcalfe is a well-known man-about-town in occupied Paris. He's also a minor asset in the US's secret intelligence forces in Europe. Through a wild twist of fate, it falls to Metcalfe to instigate a bold plan that may be the only hope for what remains of the free world. Now he must travel to wartime Moscow to find, and possibly betray, a former lover ...1991: the Communist empire is on the verge of oblivion. President Gorbachev is a virtual prisoner, and a coup is being planned by a powerful new cabal. Stephen Metcalfe, now a retired ambassador, must return to Moscow and finally reveal a secret that has haunted him since the fall of Berlin ...a secret that might just avert a global cataclysm.