Bad Company by Jack Higgins

In the waning days of World War II, Hitler gave his diary to a young aide for safekeeping. Now it's threatening to resurface, with explosive contents: the details of a meeting between emissaries of Hitler and Roosevelt to reach an armistice and turn their collective efforts against the Soviet Union. The American representative: a close relative of none other than the current President, Jake Cazalet. Powerful enemies of Cazalet will do anything to get their hands on that diary-and it is up to White House operative Blake Johnson, together with his colleague in British intelligence, Sean Dillon, to make sure they don't. . . .

Filled with hairpin twists and high-tension action, with characters as dark and surprising as any he has created, this is Higgins working at the peak of his powers.