Join the shy but brave mouse Bernard and his glamorous partner Miss Bianca – two tiny heroes on a great big mission to save a young girl named Penny, who has sent an urgent call for help. Taking off on the wings of their trusted albatross friend Orville, Bernard and Bianca soar to the marshy swamp of Devil's Bayou. There, they find themselves on the riverboat hideout of Madame Medusa, who needs Penny to retrieve the world's largest diamond.