Jackie O' (Parker Posey) is a mentally unstable woman who thinks she is Jackie Kennedy, lives at home with her mother (Mrs. Pascal), and her younger brother Anthony (Freddie Prinze Jr.) who are also pretty mentally bent.
It's Thanksgiving day and the family is waiting for Jackie's twin bother Marty (Josh Hamilton) to return home from college for the holiday. Marty shows up with an unexpected guest, his new fiance Lesly (Tori Spelling). Marty's mom and sister do their best to make sure Lesly knows she's not welcome. During a very strange night we discover that Mrs. Pascal murdered her husband years earlier and buried him in the yard. We also learn that Jackie is in love with her brother and that they used to have sex together but Marty justifies it saying having sex with your twin is no different than masturbation.
After Lesly discovers that her finance was involved in incest she turns to Anthony, the younger brother, and sleeps with him while the twins sleep together down stairs. Jackie, who doesn't want to lose her twin to Lesly asks her brother to once again rein-act the Kennedy assassination like they used to do as children and she kills her twin with a loaded gun. Unable to handle the insanity Lesly runs from the house to go home.
We assume Marty will be buried in the yard next to his father.