Nicholas Marlow, an English engineer engaged to a young doctor, one day, out of the blue, loses his well-paid job. After several months of sheer desperation, he is offered by an English armament manufacturer the post of the firm's representative in Italy. Able to speak some Italian, Marlow gladly accepts, secretly deciding that he will quit the job again as soon as possible to go back to England and get married.
On arrival in Milan, he realizes that there is a huge backlog at his office, and that both Bellinetti, his personal assistant (male), and his secretary (female) are highly inefficient co-workers. What is more, a lot of his time is diverted by the Italian authorities, to whom he has to report on a regular basis and who eventually inform him that they have misplaced his passport so that he is temporarily unable to leave the country.
There is growing uneasiness on Marlow's part when he happens to notice that his private correspondence with his fiancée has been steamed open. When he makes friends with Andreas Zaleshoff, an American businessman of Russian descent whose office is in the same building, he learns from the latter that Bellinetti is an agent for the OVRA and watching each and every step Marlow takes, and that his predecessor's accident—he was run over by a car in a dark and foggy street of Milan—was in fact cold-blooded politically motivated murder. On top of all that, Marlow is contacted by a General Vagas who informs him that he has no choice but to work as a Yugoslav spy.
There is no way Marlowe could legally leave Italy, especially after an arrest warrant has been issued for him by the authorities. Assisted by Zaleshoff, he succeeds in making his escape from Milan. Together, the two men embark on a several day long odyssey through the North of Italy—by train and on foot—until they finally, in the midst of a snowbound forest, reach the Yugoslav border. (Their flight takes up more than one third of the novel.) From Zagreb, Marlow can safely travel home to England.