When David Seville goes off to Europa on a business trip, the Chipmunks, Alvin, Simon, and Theodore are left at home with their babysitter, Miss Miller.
[FYI: part #4 of this movie moves very very fast.]The chipmunks start school for the 1st time after Dave ends up in the hospital. They have a chance to save the school's Musica department, but they're competing against the Chipettes.