Paris. 1910. A horrible monster that resembles a giant insect catches up fear in the whole of France. A shy projectionist and a tireless inventor begin to hunt for him. In this pursuit they get acquainted with a star of cabaret, a mad scientist and his clever monkey, and finally the monster itself that is not so scary. Now harmless, like a flea, the monster is looking for his new friends’ protection against a harmful chief of the city police.