Le 84 prend des vacances.

Gaston Bernod is a Parisian bus driver. Honest, upright and hard-working, he is held in high esteem by his superiors. Gaston has always pampered "his" bus, going as far as to equip it with a fuel-saving device of his invention. Very close to his vehicle, he may have somewhat neglected his wife Paulette, who lets herself got round by the smooth words of Pierrot. The gigolo has indeed managed to persuade her to follow him to the Mont Saint-Michel, "a wonderful nest for their burgeoning love" as he says. The trouble is that Gaston, while driving his dear 84, catches sight of the car, and suddenly aware of his misfortune, sees red. He immediately sets off in pursuit of the culprits, involving his load of helpless passengers in the chase.