L'Ennemi dans l'ombre(1960)

The director of the French Ministry of the Interior summons Serge Cazals, an Interpol agent, to unmask the leaders of an organization that sells military intelligence and has just made a name for itself with the assassination of Secret Service ace Georges Dandieu. Cazals is soon spotted by his adversaries and dangerously threatened. Through an intermediary in the organization, he obtains a telephone number that leads him to various leads, but to no avail. He then decides to set a trap, with the help of his friend Violaine.