Theodore goes on a diet so he could go on a date with a pen pal, who is also one of Alvin's biggest fans. Things go wrong when Alvin finds out that Theodore's date is actually the daughter of a famous film director. Alvin then takes her out instead, breaking Theodore's heart. In order for Alvin to make it to his play and the date, Alvin gets Theodore to switch back and forth to his play and on his date.