Montmartre in the summertime. A group of street urchins idles outside while the other kids of the neighborhood are away on holiday.To keep the gang busy, Pivolo, their leader, has an idea : they are going to kidnap Aunt Faguet's doggy. Just for the fun of it. A few days pass after the crime is accomplished and one of them suddenly realizes that a reward is being offered by the aunt to anyone who would bring her her pet back. Mademoiselle Hélène, the kind-hearted social worker, does it for them and gives them the reward money, which is instantly exchanged for lollipops, nougat and merry-go-round and cinema tickets. So, why not continue? That's what they do, abducting several dogs, until they realize they are becoming ... too rich! They can't buy themselves luxurious gifts or else their parents are bound to suspect something. Instead, they decide to do good by helping poor people around them. One day, Pierrot, a member of the gang, gets run down by a cyclist and becomes blind.

In the Mouffetard district of Paris, Jérôme Crainquebille, an affable four-season merchant, is stopped by a police officer and taken to the station, unjustly accused of shouting "Mort aux vaches!" ("Death to the cows!"). When he returns to work after a fortnight's detention, he is ostracized by his neighbors. Lonely, Crainquebille sank into despair and alcoholism. His life in prison seemed sweeter, and his attempts to return were in vain. He owes his salvation to the affection of a local kid.

The daughter of a foreign diplomat in Paris is courted by two men. One of them entrusts her with a harmless commission for Poland, as she has a diplomatic passport. But it's a trap, and the girl is forced to work for Eastern spies.