Edward Royle is the head of a well-known chemical manufacturer in England, which he has inherited. He is engaged to the daughter of his father's former partner, Phrida Shand, who lives with her mother. One night he is asked by his friend, Sir Digby Kemsley – a very famous railroad engineer, to come to his flat to discuss something although Kemsley is quite mysterious on the telephone. Royle visits, then returns home only to be summoned again by Kemsley, this time imploring him to return at once. Royle finds a gentleman in Kemsley's place who is clearly not Kemsley, or is he? Kemsley asks Royle to trust him but that night, a young woman is murdered at Kemsley's flat. Kemsley has disappeared. Royle discovers that his fiancé was in Kemsley's flat at the time of the murder and is obviously hiding something. Once again, Le Queux takes us through a maze of intrigue and locations in Europe.