A struggling young writer, Nicholas Whistler, is sent on a seemingly innocent commercial assignment behind the Iron Curtain. On his arrival in Prague, everyone - including his beautiful chauffeuse, Vlasta - believes the Czech-speaking Nicholas to be a spy. It takes much time and adventure for him to realise it, but when he eventually discovers that he has been plunged into the world of international espionage, he is numb with horror. With his contacts gone, he is on his own, and must escape arrest and flee to England. But the secret police are close behind him…