Four years after the events of , Alvin, Simon, and Theodore, along with the Chipettes – Brittany, Jeanette, and Eleanor – set up a surprise birthday bash for Dave that also serves as a good-luck and going-away party for the Chipettes, who are scheduled to be guest judges on "American Idol". Alvin invites and hires many people and celebrities to the dismay of Simon before Dave returns home in dissatisfaction. Nevertheless, Dave agrees to take them to mini-golf, and meet Samantha, the woman he has been dating for the past few months. While the Chipmunks like Samantha, her son Miles is a bully who physically abuses the trio. Later, the Chipmunks find an engagement ring in a bag Dave brought home and believe that he is going to propose to Samantha. Realizing in horror that Dave and Samantha getting married would make Miles their step-brother, they try to steal the ring, but are unsuccessful.