The Dark Tunnel — Ross MacDonald

DEAD MAN'S CHOICE
Doctor Robert Branch was a university professor, not a secret agent. But his best friend was dead and Branch knew that it couldn't have been suicide. He was also certain that the murder had been arranged by a Nazi espionage group operating on campus. The only trouble was, no one would believe him. Branch knew that the Nazis would have him eliminated as soon as it was convenient. He'd even narrowed his choice of executioner down to three: a psychotic homosexual, a respected educator -- and the woman he loved . . .