Somewhere in Paris, in the 1960s. A young boy named Nicolas gets into all sorts of mischief with his friends. Some unintentional, some intended. Matters get worse when Nicolas, a single child, thinks his mother is pregnant and a baby brother is forthcoming. Thanks to his friends ideas, he believes this means his parents don't love him anymore and will abandon him. He and his pals embark on several schemes to raise 500 francs to have the baby kidnapped and left in a jungle. But before any drastic consequences are successful, Nicolas learns how nice it is to be a big brother. Then he discovers his mother isn't pregnant, and is upset about that. His parents eventually have a baby, which Nicolas looks forward to, except he gets a sister instead, and tells his parents he should have asked for a puppy