The story of Alana Kane and Gary Valentine growing up, running around and going through the treacherous navigation of first love in the San Fernando Valley, 1973.

After they are forced to live next to a fraternity house, a couple with a newborn baby do whatever they can to take them down.

Composer Peter Bretter (Jason Segel) is in a five-year relationship with actress Sarah Marshall (Kristen Bell), who stars in a ''CSI: Crime Scene Investigation''-like television show titled ''Crime Scene: Scene of the Crime''. One day, as Peter stands stark naked in their apartment, Sarah announces that she is breaking up with him. Devastated, and unable to banish his grief through one-night stands, Peter takes a trip to Hawaii. However, the vacation is ruined when he learns that Sarah and her new rock star boyfriend Aldous Snow (Russell Brand) are also guests of the resort. Taking pity on him, hotel concierge Rachel (Mila Kunis) offers him an expensive suite for free in exchange for cleaning up the room himself.

Mac and Kelly are trying to sell their home with the arrival of another baby. A couple, Eric and Jessica Baiers are looking to buy; the realtor tells Mac and Kelly that their house is in escrow for 30 days. Meanwhile, Mac's friend, Jimmy, and his once-again wife Paula are also expecting a baby. At the Phi Lambda sorority, Shelby, a freshman, learns that sororities are not allowed to host parties, and can only attend frat parties. Shelby goes to a frat party and meets two other freshmen, Beth and Nora. They are disgusted by the sexist and perverse nature of the party and leave. Bonding over their dissatisfaction, the trio decides to set up a new sorority, Kappa Nu, to host their own parties.