In 1960s Paris, a young boy named Nicolas and his friends get into all sorts of mischief, both intentional and unintentional. Matters worsen when Nicolas, a single child, thinks his mother is pregnant and a baby brother is forthcoming. A friend of Nicolas's has a baby brother and thinks brotherhood is horrible. Thanks to his friend's ideas, Nicolas 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. When he discovers his mother ''isn't'' pregnant, Nicholas is upset. Eventually, his parents have a baby, which Nicolas looks forward to; however, he gets a sister instead of a brother and tells his parents he should have asked for a puppy.