In early 20th century Paris, shy projectionist Emile and his enthusiastic inventor friend, Raoul, accidentally create a monstrous yet gentle creature during a botched experiment at a scientific laboratory. The creature, who has the talent for music and a tender soul, gets loose in the city, causing widespread panic and misunderstanding due to his frightful appearance. Emile and Raoul, grappling with the consequences of their actions, embark on a mission to find and protect the creature before he is captured by the authorities. They soon discover the creature hiding in the cabaret of their friend Lucille, a beautiful and kind-hearted singer.

Lucille, who sees beyond the creature's appearance, names him Francœur and helps disguise him to blend in with her performances. As Emile, Raoul, and Lucille bond with Francœur, they uncover his exceptional musical gifts, which win the hearts of cabaret patrons, defying the city's fear of him. Their determination to keep him safe leads them through numerous challenges, including evading the relentless inspector Maynott who is bent on catching the creature for his own glory. The group's adventure weaves through a visually rich Parisian landscape, culminating in actions that highlight themes of friendship, acceptance, and the transformative power of music.