The film is set in 1910; the story beginning by documenting the flooding of the River Seine that year.
Shy projectionist Emile has a passion for film and is in love with his co-worker at the cinema, Maud. His friend, an exuberant inventor and delivery driver, Raoul, picks him up from work to transport him in his bizarre vehicle (called "Catherine"), to obtain a new belt for his projector. In purchasing a new belt, Emile also buys himself a new camera, which is almost stolen by a thief. The story also introduces Lucille, Raoul’s childhood friend: a cabaret singer at the club L’Oiseau Rare ("The Rare Bird"), whose aunt Carlotta tries to marry her to the wealthy Police Commissioner, Victor Maynott. One evening, Raoul brings Emile to make a delivery to the Botanical Gardens. In the absence of the Professor who works there, the place is guarded by his assistant, a proboscis monkey named Charles. Here, Raoul experiments with an "Atomize-a-Tune" mixture which temporarily gives Charles the voice of an opera singer and an unstable "super fertilizer" which instantly grows a sunflower seed into a giant sunflower, which topples towards Raoul and Emile. In the ensuing disorder, an explosion occurs and the two chemicals are mixed. Everyone is unscathed, but Emile is convinced he has glimpsed a monstrous creature, a photo of which later appears in the newspapers…