In producing The Last Exorcism, horror master Eli Roth began with the premise that no one can top The Exorcist.

Roth, who began his directing career with Cabin Fever in 2002 and went on to make Hostel, told CBC's Q cultural affairs show thatThe Exorcist remains one of his favourite movies.

"You don't top the Exorcist — you respect that as the scariest thing ever," Roth said in an interview Thursday from Toronto. "But you do something completely different that's unique in the canon of exorcism films and make the scariest film you can."

The canon of exorcism films is a minor one, because although vampires come and go with varied degrees of success, no film featuring exorcism has made much of a splash since the 1973 smash hit.

Roth admits that point, but says he was lured to The Last Exorcism by a smart script, created by Huck Botko and Andrew Gurland.

"It's about a preacher going through an exorcism that goes completely wrong. It's a bit of a moralistic story as well in that he says he's been doing exorcisms his whole life ... but he's having this crisis of conscience," Roth said.

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Eli Roth, shown in March, is producer of The Last Exorcism, set for release in Canada on Aug. 27. ((Associated Press))

The twist is that the preacher has hired a documentary crew to follow him through the exorcism of a young girl as a way to expose exorcism as the scam he believes it is.

"He takes you through how he cheats the [family] and then the girl shows up in his motel room," he said. Then the father turns up, armed with a shotgun, and insists the exorcism go ahead.

"I love the idea that both the reverend and the father want to help this girl, and they're both going about it for the wrong reasons," he said.

"It's the reverend going, 'Your daughter is crazy,' and it's the father saying, 'You said we had to save her soul.'"

Directed by German-born, American-educated director Daniel Stamm, the film has little of Roth's trademark gore.

Roth, known for making low-budget movies into blockbusters, was brought in to secure the money end.

He says he has seen independent filmmaking get more difficult since he sold Cabin Fever at the Toronto International Film Festival eight years ago.

"The industry has contracted so much and financing is much more difficult …the main difference is the DVD market is gone," Roth said.

The market has been lost to piracy — which has meant producers are less likely to take risks because they can't fall back on DVD sales, he said.

"With Hostel, nobody knew what it was, so nobody looked for it. Hostel 2, there was a copy of it moved on the internet a week before it was released and there was two million copies of it [made]. That's people who go to the cinema, that's teenagers," he said, reflecting on how his sequel film lost out at the box office and in DVD sales.

The Last Exorcism is set for release Aug. 27 in Canada. Roth also appears in front of the cameras this summer as the MC of a wet T-shirt contest in Pirhana 3-D.