内容简介：
The plot of this spy-detective novel turns on a senior figure in British Intelligence, who is being blackmailed by an American spy. The blackmail material, a photograph showing the Intelligence man as a former Nazi officer, is concealed in a travel book called Bannerman's Guide taken by a young British diplomat on a Danube River cruise from Vienna to the Black Sea and back. As several people are carrying other copies of the book, the story turns on who has possession of the key copy, which the American spy hopes will reach the hands of KGB agents at some undetermined point during the cruise. Various individuals are also keen to get hold of the key copy. These include an American double agent posing as a collector of folk music, and an agent of Siegfried, an organization that materially assists former Nazis. As the cruise progresses, mysterious incidents connected with the guide book occur at each of the several East European capitals along the Danube. Budapest, Belgrade and Bucharest during the Cold War era form fascinating venues and authentic background based on the author's travel experience. An English detective, Inspector Mason, begins the cruise as a genuine tourist, but gets drawn in to investigating these incidents in considerable depth, and at considerable risk to himself, until he has gathered enough evidence to be able to solve the puzzle in London. Who is carrying the key copy of the Bannerman, the significance of the material it contains and the unmasking of the spy form the intriguing climax to the story. Something of a genuine holiday atmosphere on the boat is maintained throughout, including a romantic interest and a rivalry between Mason and the young diplomat over oneof the women passengers.