A curious wood mouse, Maurice decides to explore the opera house, which glimmers like a giant lantern from across the lawn. Lured by beautiful music, he sneaks in for a tour of the opera house's rehearsals, wardrobe room, restaurant, and orchestra pit.

The uninvited guest causes a great commotion, triggering a wild chase. Luckily, a gentle caretaker understands that even a little mouse can yearn for music.