The peasant Adémaï, returning home, gets lost in the forest and knocks down a border post. In his haste to replant it, he installs it upside down.

The basic premise: A retired bus driver fulfills his lifelong dream of providing an extended "voyage surprise" (the title is translated as "Mystery Tour") for unsuspecting vacationers. They soon realize, while riding in the old man's home-made bus, that he hasn't bothered to plan any kind of itinerary. As a result, they end up in completely preposterous situations, of course. Voyage surprise!