Naive and good-hearted Léon Ménard arrives in Paris, determined to find work in the capital. In a café, he meets Bob, a seedy guy, who helps him to get a job. On cloud nine, the ingenuous young man, does is unaware of how Bob manipulates him. Having become the night concierge of a hotel, the thankful Léon lets Bob and his accomplices get into the pace. Jewels are stolen as a result.When he is accused, Leon refuses to incriminate his "friend". Fortunately, Charlotte, Léon's fiancé, manages to find evidence of Bob's guilt and thanks to a premium paid by the diamond dealer the two lovebirds can buy a grocer's shop and tie the knot.