Cornelius, who trained as a spy during the war, is asked by his old boss to track a new code being delivered to Bruno Rankel, a former organiser of the Hitler Youth now operating in England. He follows the courier, Walter Speyr, from the Liverpool docks to a pawnshop, where he sees the pawnbroker hand him a card, then to London by train. He searches Speyr's room at a seedy boarding house for the code, only to be caught by Speyr, who knocks him out.
Having caught a glimpse of the number on the pawnbroker's card, however, he discovers that Speyr is to meet a gallery owner called Wirth at his hotel, the Astoria. That evening, spying from behind a newspaper, he sees a dashing golden-haired Englishman join them. He takes the opportunity to search Wirth's room, and is again caught, this time by the chambermaid, Florrie. He persuades Florrie he is not a thief, but an anti-Nazi agent, and appeals to her patriotism to keep an eye on Wirth for him.
Following Speyr and the mystery man to a room in a different hotel, he hears a music box, and a choked cry. When the mystery man leaves, he finds Speyr strangled on the bed. There is no music box, but he sees a cigarette lighter with the initials J.Y.E. Just in time to avoid discovery, he escapes through the window, taking the lighter and Speyr's papers. The only clue in the papers is a postcard making a date at the Villa d'Este, a restaurant in Soho. There Cornelius meets a charming Englishwoman, Miss Jackson, who may have been waiting for Speyr. He finds it difficult to suspect her, but makes arrangements to stay in touch. Later he meets Florrie in a teashop and she gives him information about Wirth's contacts, including one Jimmy Earle, possibly the killer.
From the newspaper report of Speyr's murder, Cornelius discovers that Speyr was actually Carl Becker, a former German prisoner-of-war who had escaped from a farm in Wales during the war. He travels down to Llandfrith to interview the farmer and discovers that two people may have been involved in the escape, a captain who was later discharged and a land girl. Back in London he narrowly escapes being killed by a car, and realizes that he is being watched. Both he and Florrie are in serious danger.
The review of this Book prepared by Maureen Evans