Young American Reno Davis, in Paris, is engaged by the lovely widow Anne de Villemont as a tutor for her precocious 8-year-old son, Paul, and takes up residence in a mansion already crowded by her family, servants, and other people such as psychiatrist Hubert Morillon, whose patient, the mistress of the house, drinks heavily to allay her premonition that Paul is the object of a kidnaping plot. Reno's suspicions become aroused, and after his friend Louis Le Buc is murdered and the de Villemonts disappear, he discovers their true identity as the core of a rightwing secret society bent on the overthrow of the French Government and the annexation of Algeria. Under suspicion for the murder, he finds Anne, who is being held captive, and the two flee Dijon by train for the Villa Frascati in Italy, where Paul is rumored to be held captive. There Reno uncovers an agents' list coveted by Morilion, who is in reality Sebastian de Villemont (Anne's "dead" husband who conceived his own demise at the hands of terrorists in order to return secretly to Paris as the head of the organization). In a struggle for the list, de Villemont is killed by one of his own henchmen and Reno escapes with the now legitimate widow Anne to Rome to save Paul from the designs of the organization's rival pretender to power, Charles Leschenhaut. Leschenhaut agrees to exchange the boy for Reno's list, but instead he orders Paul to avenge his father's death, for which he has claimed Reno responsible. But Paul is affected by memories of his early friendship with the American and turns the gun on Leschenhaut, who backs fearstruck through a railing and plunges to his death.