When Cole stays up past his bedtime, he discovers that his hot babysitter is part of a satanic cult that will stop at nothing to keep him quiet.

Bianca's universe turns upside down when she learns that her high school refers to her as a ‘DUFF' (Designated Ugly Fat Friend). Hoping to erase that label, she enlists the help of a charming jock and her favorite teacher. Together they'll face the school's mean girl and remind everyone that we are all someone's DUFF… and that's totally fine.

After arguing with his girlfriend, Ali, Tyler lands in the arms of sexy new girl, Holly. The next morning, he finds that not only does Ali agree to take him back, but Holly is a new student at their school and is dead set on her new man.

Through a series of misunderstandings, Alvin, Simon and Theodore come to believe that Dave is going to propose to his new girlfriend in New York City - and dump them. They have three days to get to him and stop the proposal.

Alexander's day begins with gum stuck in his hair, followed by more calamities. Though he finds little sympathy from his family and begins to wonder if bad things only happen to him, his mom, dad, brother, and sister all find themselves living through their own terrible, horrible, no good, very bad day.