In an interesting precursor to the later I Spy television series, the novel follows the activities of a young British tennis professional, Mervyn Amory, who is spending the season in Monte Carlo. While traveling from Paris on Le Train Bleu, he meets an Italian secret agent who is carrying documents which show the treachery of the dictator Matorni.
Interestingly, this novel was written in 1928, which was only 2 years after Mussolini assumed dictatorial powers over the country.