Valuable documents have been stolen from a British laboratory. Slim Callaghan is sent to investigate the theft. But his tracks soon lead him to the welcoming skies of the Côte d'Azur. There, he decides to infiltrate a network of aristocratic spies.

A ship, La Circé, has sunk and it might possibly be criminal . The vessel belongs to Storata ,who asks the insurance company for a hundred million Francs .Callaghan is working for them and he investigates on dry land and on the sea. The brilliant detective discovers that Storata has scuttled his ship himself to swindle insurance.

Carlos, a weapons trader, is struck by his resemblance to a certain Slim. Wishing to take advantage of this situation, the mafioso asked the latter to be the commander of his ship.

Slim Callaghan investigates the theft of the famous Upper Sangha diamonds. Disguised as a Salvation Army auxiliary, he boards a luxury yacht where a transvestite party is being held. During an illusionist's trick, Callaghan manages to steal the precious diamonds, but the thief escapes.