On the suggestion of Jimmy's friend Craig, the popular students tell him to search for Appleday's frozen brain in the ride "Tux's Arctic Adventure".

Jimmy unwillingly goes there and bumps into Milt's middle-aged, clumsy son Sonny, who is attempting to retrieve the brain.

With the help of his crush, Craig's sister Robin, Jimmy learns that Sonny unwittingly ruined the characters' popularity through his own ideas.

With Milt's creativity and imagination, Jimmy becomes immensely popular but no longer has time for school or his friends.

He devises a plan to modify Crocco's Train to include several dangerous devices that will decapitate Jimmy.

In an epilogue, while Jimmy is leaving for school, Sonny attempts to extract his brain with a crane-like device but misses.

Emily Ashby of Common Sense Media called it a "brain-swap tale [that] will have tweens' eyes rolling".