Lionel Scampion, British consul in Naples, has been stabbed to death while bicycling through the piazza of the Porta Carmine. According to his sister, he had no enemies. The Neapolitan police suggest he was murdered by a bicycle-racing rival. In Naples, every mystery is attributed to the Camorra, a powerful criminal society; could its members be involved? Scampion enthusiastically backed the Italian invasion of Libya and befriended army officers of the newly formed Italian Bicycle Brigade. Now the Foreign Office in London has heard that international politics emanating from Rome might have been involved. Seymour of the Special Branch is sent to find out the motive for the murder and, incidentally, to identify the culprit.