In a factory working for the National Defense, an employee steals a prototype. In charge of the investigation is Francis Coplan.

The directors of a company threatened by a railroad construction project in Africa decide to have the General Secretary of the Franco-African consortium killed. Géo Paquet, known as "Le Gorille", a DST spy, attempts to infiltrate the gang.

An unpopular school teacher is left over Christmas with some of his boys.