Dave is stuck at the studio all night to mix the boy's next album. But he leaves a Babysitter to after the Chipmunks while he's gone. After watching a detective movie, Alvin suspects her to be a murderer.

Uncle "Adventure" Willy

Micky, a new Irish boy at school, claims that he has his very own leprechaun. The Chipmunks are keen to investigate.

Theodore develops a crush on a girl in his class named Juliet. Wanting some expert advice, Theodore asks Alvin for his help. Unwillingly, Alvin says a romantic line that Juliet overhears and she ends up developing a crush on Alvin instead of Theodore.

Brittany tries out for Alvin's football team. To get even, Alvin joins her cheerleading squad. Will they set aside their differences and help each other succeed?

Alvin plays one prank on Theodore and gets him to eat a dog biscuit. To get even, Theodore, with Simon's help, plays a trick on Alvin and makes him think that his younger brother is actually turning into a were-dog.

By a fluke, Alvin actually passes his math test whereas, Simon mysteriously fails. Afterwards, Alvin believes he is psychic, and so does everyone else, except Simon.

The boys disobey Dave and instead of seeing a kid's movie, they go in and see a horror movie. The movie ends up scaring the Chipmunks out of their wits. All night, the boys think that Hideous Harold, the creature from the horror film, is after them.

Alvin is tired of being treated like a kid and trades place with Dave for a day to feel what it is like to be a grown-up.

Simon transforms into the legandary Batmunk. This is a play off of Batman. Batmunk must stop an evil plan that involves a large toy heist.