In the movie Barbie stars as a country girl, Corinne, who dreams of being one of the famous Musketeers, the protectors of the French royal family, just like her father, D'Artagnan. Now seventeen years of age, Corinne asks her mother to let her go to Paris to become one. Although somewhat worried about the dangers, her mother is supportive and gives Corinne her blessing, as well as a letter to Monsieur Treville, the captain of the Musketeers and an old friend of her father's.

The next day before leaving, Corinne's mother reminds her about what her father use to say: "True courage is pursuing your dream, even when everyone else says it's impossible." Hugging her mother goodbye, Corinne sets off for Paris with her kitten, Myelle, and Alexander, D'Artagnan's old horse.

when she arrives in Paris, Corinne watches four Musketeers displaying their skills. She tells them about becoming a Musketeer herself and asks them where to find Treville. They tease her as a mean dog, Brutus, knocks her over and steals her letter. Attempting to get it back, Corinne and Myelle chase him into the Musketeer headquarters, where Treville is talking to Philippe, the kingdom's regent and Brutus' owner. When hearing why she is there, Philippe scoffs at Corinne's dream to be a Musketeer, saying girls don't possess the proper skills. However, Treville kindly invites her inside.

Corinne feels triumphant at first, but she is disappointed when Treville says she's not ready for active duty, but he tells her to keep practicing and that if she needs anything, to come to him. After leaving, Corinne sits outside with Myelle when Brutus sneaks up on them again and chases after Myelle. While in pursuit, Corinne literally bumps into three other girls: Viveca a fashionista, Aramina a dancer and Renée a violinist.