British Intelligence dupes an unemployed writer into thinking he's an industrial spy.

Young Nicholas Whistler, an out-of-work British writer, is hired as a junior executive to glass manufacturer Colonel Cunliffe. Nicholas accepts the position because the pay is high, but what he does not know is that Cunliffe is actually head of British Intelligence and he will be used as a secret agent. Nicholas, who speaks Czech, is told to go to Prague and pick up from a contact at the State glassworks some vital information. He understands that the mission must be done under cover because open trade with Iron Curtain countries is still impossible. Nicholas' password with his Prague contact is "hot enough for June." He is met at the airport by Vlasta Simenova, his chauffeur, who is actually a counterspy working for her father, head of Czech Intelligence. Nicholas and Vlasta have fallen in love by the time he has acquired the paper from his contact, who informs Nicholas that they are both spies. After eluding the Prague police, Nicholas finds refuge in the British Embassy, and he gains passage back to London when embassy officials exchange him for a British-held spy. He is delighted when he is joined on the return trip by Vlasta, who is being sent to London on a "trade" mission.