Tired of war, they set off on an adventure. The 20th century begins and the children play in the garden until the end of summer. Accompanied by his cousin Louis, his younger brother Ernest, and Marthe, the mischievous little girl, Paul will travel all the way to the Amazon to discover the mystery of Venus.

Mathilde, aged 9, enjoys her last day of summer holidays at the seaside with her group of friends. Her father falsely interprets one of their games.