Robin Bellefeuille is a postman in Saint-Tropez. A factor in the old methods: riding his old bike, he makes his round in peace, never refusing to stop to chat or have a drink with his friends. Robin is also a local personality. Not only because everyone has known him for a long time, but because he is the president of an association of environmentalists who strive to protect the region from all forms of pollution. Pollution, it could well come from local politicians. Chantal Sagazan, the mayor, and the deputy Lespinasse are planning, in fact, a real estate operation: the construction of a casino, which will destroy nature, perhaps, but will fill their pockets. Robin is therefore not in favor with Mrs. Sagazan. This does not help the affairs of Julien Bellefeuille, his son, a postman too, who lives a tender idyll with the daughter of Madame le Maire. While Julien, Patrick and their friends are cleaning the beach and the countryside, Robin and his old companion, Gendarme Ficelle, try to thwart the plans of the speculators. Robin has a terrible weapon, the crippling cry: he just has to push an ah! resounding so that its surroundings are brutally frozen on the spot. He does not fail to use it. And, with Ficelle, he succeeded in driving away a representative from the Ministry of Finance, who was involved in the casino business. Chantal Sagazan suspected that Robin was making his plans fail. She decides to disgust him by blasting the little cabin where he stores his fishing gear. Fate: the explosion reveals a significant oil deposit. The "Robin Oil Company", of which Ficelle is the co-director, allows the postman to make a fortune. As for Julien, he can finally marry the one he loves.