Alex, Kelly, Benji, Ryan, Pooh, Littlefoot, Ash, Stan, Alex, Benny, Bobby, Cindy, Oliver, all their characters and their Auntie Anabella go to visit their Great Uncle Rubato in his Marvelous Musical Mansion where the music boxes come to life, the hat rack sings and dances, and the door knocker requires you to solve a riddle before you enter. In the darkness of the night, however, several small but important items vanish, requiring the children to locate the thief. Each segment teaches the viewer about musical theory or terminology.
- "My Aunt Came Back (crossover)"
- "She'll Be Comin' Round the Mountain (crossover)"
- "How Do You Do?"
- "My Hat, It Has Three Corners"
- "The Orchestra Game Song"
- "Tap-A-Cappa (crossover)"
- "The Ballerina's Waltz"
- "The Doodle-Dett Quintet (crossover)"
- "Rockin Robin"
- "The Marching Song (crossover)"
- "Viva La Campagnie (crossover)"
- "The Melody Song (crossover)"
- "The Magic of Music (crossover)"
- "Hickory, Dickory Dock"
- "Round the Clock"
- "Oh Where, Oh Where?"
- "The Clapping Song"
- "Reuben and Rachel"
- "Hey Diddle Diddle"
- "Oh Were, Oh Where? (reprise)"
- "The Magic of Music (reprise)"
- "When the Saints Go Marching In (crossover)"
- Greg, Marcia, Peter, Jan, Malcolm, DJ, Emily Yeung, Daniel Cook, Richelle, Mighty Morphin Power Rangers, Earl and his family, Reese Ambler, Rydell, Becky, Dylan and their friends, Alan Grant and his friends, and the rest of the characters will guest star in this film.