Proud of his status as a dunce, Toto constantly annoys his teacher with mischievous jokes and puns, to the delight of his classmates. An inveterate practical joker, Toto proclaims his innocence when a catastrophic event occurs at the inauguration of a museum, built to the glory of entrepreneur and aspiring mayor Roger Justin-Petit, for whom his father works. When Toto is threatened with being sent to a strict private institution, he sets out to discover as quickly as possible the real culprit responsible for the sabotage at the museum. To do this, he gets help from Igor, the director's son. In exchange, Igor, a model student who’s on the dull side, asks Toto to show him how to be funnier.