The Venetian Affair — Helen MacInnes

Set in the 1960s during the Cold War, this is a captivating espionage adventure from “the queen of spy writers” who has been compared to Graham Greene and Ian Fleming (Sunday Express).
 
While on assignment in Paris and Venice, an American journalist works desperately to expose Communist espionage activities . . .

Fenner burned Rosenfeld's message, reminding himself wryly that he was behaving in the very best tradition. This was a game not too difficult to learn, he thought. A game? A game in deadly earnest. A vacation in Venice that was grim business. A girl constantly beside him who wasn't his. How the hell had he walked into this upside-down world? Where, he wondered suddenly, would Venice lead?