On October 30, 1977, amateur criminals Karl and Richard Wick attempt an armed robbery at a gas station/horror museum, but are killed by the owner, Captain Spaulding, and his assistant, Ravelli. Later that night, Jerry Goldsmith, Bill Hudley, Mary Knowles, and Denise Willis are on the road in hopes of writing a book on offbeat roadside attractions. When the four meet Spaulding, who is also the owner of "The Museum of Monsters & Madmen", they learn of the local legend of Dr. Satan. As they take off in search of the tree from which Dr. Satan was hanged, they pick up a young free-spirited hitchhiker named Baby, who claims to live only a few miles away. Shortly after, a mysterious figure appears hidden in some overgrowth and shoots out their vehicle's tire with a shotgun. The group thinks it is just a blown out tire and so Baby takes Bill to her family's house to get a tow truck. Moments later, Baby's half-brother, Rufus, picks up the stranded passengers and takes them to the family home.
There, they meet Baby's family: her adopted brother Otis Driftwood, her deformed giant half-brother Tiny, Mother Firefly, and Grandpa Hugo. While being treated to dinner, Mother Firefly explains that her ex-husband, Earl, had previously tried to burn Tiny alive, along with the Firefly house after he suffered a psychotic breakdown. After dinner, the family puts on a Halloween show for their guests and Baby offends Mary by flirting with Bill. After Mary threatens Baby, Rufus tells them their car is repaired. As the couples leave, Otis and Tiny, disguised as scarecrows, attack them in the driveway and take them captive. The next day, Otis kills Bill and mutilates his body for art. Mary is tied up in a room and tormented by Otis, Denise is tied to a bed dressed up as a doll for Halloween, and Jerry is partially scalped for failing to guess Baby's favorite movie star.