Four friends head to Vegas for a 21st birthday in hopes of finding adventure, debauchery and memories that will last them a lifetime.

A gang of lovely young ladies known as the Ding Dong Ditchers terrorize a sleepy suburban town by ringing peoples' doorbells and then running away. Crazed and pathetic loser Doug has just been fired from his job, so he decides to make a stand against the Ding Dong Ditchers in order to impress Claudia, who's the attractive woman who lives right across the street. However, Doug's initially minor dispute with the Ding Dong Ditchers eventually escalates into an all-out no-holds-barred war.

Aspiring actress Amelia begins her 25th birthday by breaking up with her boyfriend, and things only go downhill from there. After visiting a dubious psychic for advice, Amelia sets off on a bizarre adventure to find money for rent and possibly love.

On the eve of her 19th birthday, Nina finds out that she has been cursed since ancient Roman times by Emperor Justinian. She carries a plague that can wipe out the human race. The Book of Fire reveals that Nina can choose to live and infect millions, or avoid the fate by spending eternity in purgatory. She has three days to decide, and so Nina has no choice but to make her own destiny.