Plot

A 3D-animated movie set in Paris in the year 1910 and centered on a monster who lives in a garden and his love for a beautiful, young singer.

Paris, 1910. Emile, a shy movie projectionist, and Raoul, a colorful inventor, find themselves embarked on the hunt for a monster terrorizing citizens. They join forces with Lucille, the big-hearted star of the Rare Bird cabaret, an eccentric scientist and his irascible monkey to save the monster, who turns out to be an over-sized but harmless flea, from the city's ruthlessly ambitious police chief.—The Film Catalogue

Parijs, 1910. Shy movie theater operator Emile accompanies his boisterous friend, would be-inventor Raoul, who delivers goods by sunflower oil-powered truck, with a shipment to an absent botany professor's lab where the devoted monkey assistant Charles fails to prevent flippant Raoul experimenting against clear written warnings with seeds and super-fertilizer to accidentally create a giant plant and a monstrously magnified flee that breaks trough the hot greenhouse roof. The roofs-leaping monster causes panic throughout the inundation-plagued city, so police prefect Maynott considers it the ideal diversion from regular police problems and an opportunity to enter the mayoral election race as the hero who caught it. Raoul has a furiously denied mutual crush -like Maynott- on nightclub singer Lucille, who meets the monster, finds it cute and gets the gang to try hiding it, and help it escape when Maynott finds its trail and won't be stopped, not even by grave danger for people.—KGF Vissers

In picturesque and bustling 1910s Paris right after the Great Flood, two friends--the timid projectionist, Emile, and the delivery-man by day and inventor by night, Raoul--are about to embark on the adventure of a lifetime, when a delivery to the Botanical Gardens ends up in total catastrophe. Now, a mysterious and fearsome creature with glowing red eyes roams the dark alleys of the metropolis, and only the Rare Bird's lithe cabaret singer, Lucille, seems to have the power to scratch beneath the surface and tame it. As the news of the terrible Parisian beast spread like wildfire, the hulking guitarist with the lovely singing voice, Francoeur, lands a job as a musician in Lucille's show--while at the same time--the mayor and every gendarme in town struggle to solve this intricate puzzle. Is there, indeed, a hideous monster in Paris?—Nick Riganas

In 1910; the story begins by documenting the flooding of the River Seine that year. Thousands of residents living near the river have already been evacuated. The residents of the city use boats or a series of wooden pathways to get across the city. The water reaches 20 feet above the normal and has even reached the foot of the Eiffel tower. Shy projectionist Emile (Jay Harrington) has a passion for film and is in love with his co-worker at the cinema, Maud (Madeline Zima). As Emile daydreams about asking Maud on a date, the belt of his projector apparatus breaks down and he has to use his own personal belt to complete the movie for the patrons of the cinema. His friend, an exuberant inventor and delivery driver, Raoul (Adam Goldberg), picks him up from work to transport him in his bizarre vehicle (called "Catherine" which runs on sunflower oil), 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 thief is defeated when he runs into Catherine. Raoul tells Emile to write Maud a letter to describe his feelings, since Emile cannot summon the courage to talk to her directly.

Lucille (Vanessa Paradis) is Raoul's childhood friend: a cabaret singer at the club L'Oiseau Rare ("The Rare Bird"). Lucille's aunt Carlotta (Catherine O'Hara) tries to marry her to the wealthy Police Commissioner, Victor Maynott (Danny Huston). Lucille promises Raoul the best seats in the house if he ever comes in with a Medal of Honor.

One evening, Raoul brings Emile to make a delivery to the Botanical Gardens. In the absence of the Professor who works there (who is now attending a conference in New York), the place is guarded by his assistant, a proboscis monkey named Charles. The Professor had left explicit instructions not to touch anything, but Raoul isn't much inclined to follow them. Raoul finds the Professor's lab inside the Botanical gardens. Here, Raoul experiments with an "Atomize-a-Tune" mixture (which was made by the professor) 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. Raoul and Emile notice that the seed started growing when it was thrown into the water, and it absorbed a large amount of water during the process. In the ensuing disorder, an explosion occurs when the two chemicals are mixed. Everyone is unscathed, but Emile is convinced he has glimpsed a monstrous creature (7 foot tall, red blazing eyes, 4 arms and spikes all over the body), a photo of which later appears in the newspapers.

An investigation is launched into the whereabouts of the creature by Maynott's second in command, Pate (Bob Balaban), but is fronted by Maynott, in the hope of popular support for his mayoral candidacy. Maynott's popularity has been sinking with the city of Paris. At the same time, he tries unsuccessfully to seduce Lucille. Emile and Raoul develop the film from Emile's camera (since he was recording inside the Botanical Gardens). They clearly see the monster they have created.

Meanwhile, Lucille is trying to find a new musician for her show, and turns down the cabaret's waiter, Albert (Matthew Geczy). Trying to vacate the cabaret, Albert stumbles across the creature and flees, terrified. Upon seeing the creature, Lucille is frightened, but hears it sing and discovers it is not dangerous but has a lovely singing voice. She therefore welcomes it, under the name of Francoeur (Sean Lennon) (meaning "honest heart"). It is then revealed that the creature is a flea that the fertilizer, in the middle of all the other chemicals in the laboratory explosion, enlarged to human scale.

During the investigation, Emile and Raoul's role in the laboratory incident is discovered. For Maynott's interest in the creature, they receive the Medal of Honor. Pate concludes that a flea from Charle's coat got mixed up in the chemicals and became the monster.

On a challenge set earlier by Lucille, Raoul uses this to get the best seats at Lucille's show at "The Rare Bird", where Francoeur and Lucille sing as a duet. After the show, Emile and Raoul congratulate Lucille on her show, but Lucille reveals the identity of Francoeur, which Albert reports to the police. Emile, Raoul, and Francoeur narrowly escape, and Albert is arrested on suspicion of lying to the police.

The following day, Maynott opens the Montmartre Funicular, which serves Montmartre and the Basilica of the Sacré Coeur. The trio, along with Francoeur and Charles, decide to feign the death of the creature. When Maynott discovers the creature hiding under the stage, Francoeur and his friends are chased through the streets of Paris by Maynott. The chase concludes at the tip of the Eiffel Tower. After a battle to protect Francoeur from Maynott, a gunshot from Maynott and Francoeur's sudden disappearance leads everyone to believe he is dead.

Maynott is then arrested by Pate for premeditated murder (on the basis that Francoeur is innocent), while Emile and Maud fall into each other's arms. Later that evening Lucille is distraught by the disappearance of Francoeur; but Raoul convinces her to sing anyway. Whilst struggling to begin, she hears Francoeur, restored to his natural size, sing in her ear. Sometime later, the absent Professor returns from his trip; and when the three friends explain the situation, he permanently returns Francoeur to human size.

Francoeur receives second billing on the posters advertising Lucille's show. Lucille and Raoul later share their first kiss in Lucille's dressing room. In a flashback, it is revealed that Raoul misunderstood Lucille's intentions when she took his toy truck as a child-she had hoped that he would pursue her.

In a mid-credits scene, Raoul, Lucille, Francoeur, Maud, Emile, Charles, Carlotta, and Pate scatter super-fertilized sunflower seeds to drain the flooded Seine. In a second post-credits scene, Maynott is shown in the same cell as Albert and the thief from earlier, forced to endure the duo's appalling singing.