Concerning the plot of Scary Movie 4, Cindy Campbell (played by Anna Faris) is a reporter who lives in a creepy old house that she suspects to be haunted. She discovers that a little boy named Cody (played by Drew Mikuska) was murdered in the house, and his ghost has been haunting it along with other malevolent spirits.
Meanwhile, Earth is being invaded by alien "Tr-iPods" that are taking over human bodies and causing chaos worldwide. Cindy teams up with Tom Logan (played by Craig Bierko), a clumsy and clueless man who also happens to be the only person who can see Cody's ghost. Together, they try to unravel the mysterious connection between the Tr-iPods and Cody's murder.
Throughout the movie, Cindy and Tom encounter various parody versions of classic horror films like War of the Worlds, The Grudge, and Saw. There are also recurring characters from previous Scary Movie films, like the perpetually stoned Brenda Meeks (played by Regina Hall) and the raunchy, foul-mouthed puppet "Trixie."
In the end, Cindy and Tom manage to defeat the Tr-iPods and solve Cody's murder, bringing peace to the house and the restless spirits that inhabit it. The movie concludes with a hilariously absurd musical number, featuring a cast of characters from all the Scary Movie films.