The scariest part of the Cobb Factory haunted house in Old Monroe is not the chain saws or mutilated corpses that lurch out from the corners; it's the back story.

The attraction's website offers a straightforward account of crazy Eli Cobb, a farmer who butchered his wife and children. Gory details are reported with a matter-of-fact indifference usually found in police crime reports:

"The carcass had been decapitated, slit open and gutted," and "Eli's chair was made of human skin, and in his bedroom chest they found a human head, four noses and a heart."

Could the story be true? Sure — and witches fly vacuum cleaners. Still, haunted-house veterans agree that a back story that is even slightly plausible gives the best attractions real bite.

"Plenty of haunted houses just have scary scenes thrown together that don't really mesh, like alien abductions next to psycho killers and monsters," says Melinda Warner, who creates the back stories for the legendary Blackford Haunt, located in her family's Ballwin home. "I'm fairly insistent that the haunt should make sense. I have had several e-mails over the years from people who have stumbled upon the site and thought the story was real."

This year, carnival workers pitch their tents in the uninhabited town of Blackford and become infested with its evil spirits. Prior years have focused on Blackford's prestigious Applewood Asylum, an exclusive home for the rich, and the manor of the Asylum's doctor, Jonathan Blackford.

"I try to make things as realistic as possible," Warner says. "I keep a timeline of all the major events involving Blackford and its doctor, including things not mentioned in the story, like the years of characters' births. This helps to lend a sense of realism to the story arc and keeps things consistent even if people aren't aware of all these details."

The back story of Red's Corn Maze Massacre in Eureka is rooted in the real-life horror story of the Times Beach dioxin disaster.

"The spill was contained and cleaned up with great speed and care — or at least everyone thought so," reads the site's story. "Strange creatures and deformed humanoid figures have been spotted in the fields. Over 100 local residents have gone missing in the past two months."

Haunted House owner Jerry Kirk patrolled Times Beach for years as a St. Louis County police officer. He also operates the Eureka Butcher.

"The back story becomes part of the entertainment," Kirk says. "To set the story in a place that really was frightening makes the experience all the more realistic. It's the bit of history that gets under your skin."