A Monster in Paris

In 1910 Paris, the Seine overflows and floods the city. Thousands evacuate as boats and wooden walkways become the main routes through town. Water reaches 20 feet above normal, even brushing the foot of the Eiffel Tower.

Shy projectionist Emile's belt breaks during a screening, forcing him to improvise with his own belt to finish the film. He is secretly in love with his co-worker Maud, which makes the moment feel even more tense. The crisis pushes the day toward a personal crossroads.

Raoul arrives in his eccentric sunflower-oil powered vehicle Catherine to fetch a replacement belt for Emile's projector. During the outing, Emile buys a new camera, which is nearly stolen by a thief. The thief is thwarted when Catherine collides with him, saving the equipment.

Raoul urges Emile to write Maud a letter expressing his feelings since he can't speak them aloud. The letter becomes a catalyst for their budding connection and for Emile's self-confidence. It foreshadows the courage they will need in the days ahead.

Lucille, a cabaret singer at L'Oiseau Rare, navigates Aunt Carlotta's attempts to marry her to Police Commissioner Maynott. Maynott's political ambitions depend on public favor, which Lucille's association could boost or ruin. She also promises Raoul the best seats in the house if he ever brings home a Medal of Honor.

Raoul brings Emile to the Botanical Gardens for a delivery to the absent Professor. They ignore explicit instructions that nothing should be touched, and the monkey Charles is left guarding the lab. The experiment with an 'Atomize-a-Tune' and a volatile fertilizer triggers chaos as sunflowers explode in growth.

An enormous seven-foot creature with red eyes is glimpsed after the explosion, though it is later revealed to be a flea enlarged by the lab incident. Emile and Raoul develop the film they shot in the gardens and catch a sighting that stirs the city. Newspaper reports begin to circulate about the sighting.

Albert the waiter stumbles across the creature outside the cabaret, while Lucille discovers it can sing and christens him Francoeur. It is revealed that Francoeur is not a monster but a flea enlarged to human size by the accident. The discovery reframes fear into wonder for the cabaret crowd.

Pate concludes the creature originated from a flea, not a real monster, and Emile and Raoul receive the Medal of Honor for their role. Maynott tries to capitalize on the incident to boost his mayoral bid. Lucille witnesses the media storm and begins shaping her career around Francoeur.

Raoul uses the Medal to secure Lucille's show as Francoeur and Lucille perform a duet to a cheering crowd. Lucille reveals Francoeur's true identity to Albert, who reports it to the police. The crowd delights in the performance even as the mystery deepens.

Maynott and his men pursue Francoeur through the streets as the trio and Charles hide. They stage a feigned death for Francoeur to mislead the authorities and escape. The chase winds through Montmartre and the main streets of Paris.

The pursuit leads to the Eiffel Tower, where a gunshot from Maynott and Francoeur's sudden disappearance convinces everyone that he is dead. The city is left stunned and the mystery lingers in the air. The friends scramble to regroup after the dramatic turn.

The absent Professor returns from his trip and, after hearing the tale, permanently restores Francoeur to human size. Emile and Maud share a moment of relief and connection, while Lucille's world also stabilizes. The group celebrates a small victory amid a city still recovering from the flood.

Francoeur receives second billing on the posters advertising Lucille's show as the night continues. Lucille and Raoul share their first kiss in her dressing room, and a childhood misunderstanding is revealed to have brought them together. The moment seals their bond and marks a new beginning.

In a mid-credits scene, the friends scatter super-fertilized sunflower seeds along the Seine to drain the floodwaters and help rebuild the city. They celebrate their teamwork with practical optimism. In the post-credits, Maynott is shown in the same cell as Albert and the thief, forced to endure their singing as a comic punishment.