"Mystery Girl" is the first and second episodes of the third season of the television series The Naked Brothers Band, which premiered as a television movie on Nickelodeon on October 18, 2008[1] to 4 million viewers for children in the 6-11 and 9-14 age groups; it was the top rated episode of the series.[2]
The Naked Brothers Band begin filming a motion picture called The Top Secret Naked Brothers Band Musical Mystery Movie.
13-year-old Nat Wolff tries to grapple why Rosalina (Allie DiMeco), aged 15, is trying to get herself written out of the script. To Nat's dismay, he later discovers that Rosalina is going to leave for a 6-month boat cruise around the world for winning a violin competition and he subsequently becomes mad at her.
Meanwhile, 10-year-old Alex Wolff panics when he finds out that he has to kiss his skateboarding buddy, Juanita (Teala Dunn), aged 11, for a scene in the film. Much to their relief, it turns out that Juanita did not have to kiss Alex—as it was just a typo by the screenwriter; instead, Juanita only has to kick him.
Christophe (Andrew Keenan-Bolger) is the stubborn movie director. He gets overthrown and replaced by Cooper Pillot, the 13-year-old producer of film.
During the time Nat is moping around, he develops feelings for his costar, the renowned actress Miranda Cosgrove, aged 15, and he feels confused after kissing her for a scene in the movie. After that, Miranda suggests that Nat do something very special for Rosalina before she leaves for the cruise.
Nat finally accepts that Rosalina is leaving and decides to perform a serenade with the band for her, by singing his self-written composition, "Your Smile", outside of her apartment.