Rosalina comes back after her music cruise, but Michel (the French guy Rosalina kissed on the cruise) also comes back, criticizes Nat's music, and kisses Rosalina which Nat sees. This causes a heated fight between Nat and Rosalina in which they break up and Rosalina quits the band.
Jeremy Fink and his best friend Lizzy must search high and low throughout the streets of Manhattan for clues to unlock the mysterious box he received a month before his birthday.
The band's next concert stop is in New Orleans where Nat reunites with a childhood friend, sending Rosalina into a jealous frenzy! Meanwhile, Alex initiates an extreme environmental movement to help save polar bears at the North Pole, but devious reporters frame him to appear as a conceited rock star who hates Santa!
The Naked Brothers Band and another band, the L.A. Surfers, find themselves competing in a "Battle of the Bands" charity event benefiting Little Kids Rock. Rosalina starts to fall for the L.A. Surfers' lead singer, Bobby Love. It annoys Nat that Rosalina hangs out with the opponent's lead singer. It turns out that Bobby is just dating Rosalina to get to Nat and is lying about everything, i.e, his British accent, not writing his own songs, etc. Nat and Bobby fight and declare at a press conference that the charity event is now a competition and the losing band's proceeds from their next CD goes to the charity.
Everybody is excited about the end of the year masquerade party at Amigos Middle School, which unfortunately coincides with the prom at Amigos High School. While the band argues over their costumes, Rosalina decides she's rather hang out with the band at the middle school dance even though she's a in high school. Nat, thinking he's doing her a favor, pushes her into going to the prom with the most popular senior, Wade Killgallen, and then immediately doubts his decision. Patrice Johnson, "the most popular freshman" is furious that Wade is going with Rosalina, and forces Nat into being her date. Meanwhile, Thomas and David pull off the prank of all pranks, and then Cooper takes the fall for his buddies, making him a hero in the eyes of Ms. Scoggins. Nat and Rosalina ditch the prom early for the masquerade party, where the Naked Brothers Band rocks the house with a performance of "I Don't Wanna Go to School".
