A widow named Blanche Montel endeavours to find a man with whom to produce a child so that she can pretend that the child was her late husband's and so inherit a fortune.

On his wedding night with Hilda Bergmann, the daughter of a swedish chemist, the young and rich american Willy Keanton is stabbed by an unidentified masked man. He kidnaps the young woman, who is found later on by the count Robert d'Arbel. The detective Jacques Miral, nicknamed « the pointed tower's ferret » is put in charge of the case. Soon, he discovers that an international bandit, Méphisto, seeks to seize the formula of a process against asphyxiating gas, invented by professor Bergmann. The struggle is tough between Miral and the uncatchable Méphisto. Monique Aubray, Keanton's secretary and engaged to the detective, the Nostradamus stallholders and the « mastiff of Bordeaux », and the famous novelist Fortuné Bidon are also involved in the case...