Microbe is a shy boy, often lost in his drawings. Gasoline is a smart, inventive kid, who arrives at school in the middle of the year. The two instantly become great friends, and as the summer vacation draws closer, they both know that neither wants to spend two months with their respective families. Thanks to a lawnmower engine and a few planks, they build their own "car" and set off for an adventure on the roads of France...