Personal Demons Take On a Deeper, Darker Meaning : DARK DEBTS by Karen Hall: Random House; $24, 403 pages

“Let me get this straight,” Jack Landry asks Father Michael Kinney in veteran TV screenwriter Karen Hall’s first novel. “You’re saying there’s something in me . . . that my body is just a shell and I’m actually this invisible . . . thing . . . that lives there? And I can be displaced by another invisible thing, which happens to be an evil thing . . . that wants to destroy me . . . by making me destroy other people?”

“Basically,” the priest agrees. Landry is possessed by a demon, which has bypassed his conscious mind to make him commit murder--just as novels like “Dark Debts,” despite their pretensions to seriousness, can’t help but reveal the pop formulas they are made of.

The advantage of formulas, at least, is that they are time-tested ways of grabbing and holding our interest. Fans of William Peter Blatty’s “The Exorcist” will enjoy this entertainment too, though Blatty wrote better prose.

Hall, whose credits include scripts for “M*A*S*H” and “Hill Street Blues,” is a sure-handed plotter. She sets two stories in motion and then, three-quarters of the way through, has them mesh with the satisfying click of well-oiled machinery.

One is the story of Kinney, a Jesuit who has been exiled to the Georgia boondocks for embarrassing the church hierarchy with his public testimony, after a previous exorcism attempt went awry, that he believes in personal devils.

Then Kinney’s beloved grandfather, an Atlanta architect, dies, leaving behind a horrifying revelation--that he and his father, the leader of a Satanist cult, had something to do with the other story: the curse that haunts the Landry family, for whom the word “dysfunctional” is hardly strong enough.

Jack Landry’s father, Will, was a beast who may have killed one of his four sons, all hell-raisers. Another of Jack’s brothers, Tallen, gunned down five Christmas worshipers in a church and was executed. Jack’s mother, Lucy, went insane after years of abuse. A fortuneteller had warned her: “You’ve taken on a debt you don’t know about. You’ll pay, your children will pay, a lot of people will pay, for a long time.”

Jack’s youngest brother, Cameron, seemed to escape the curse, becoming a successful crime novelist, but he has suddenly flipped out, robbed a Los Angeles liquor store, killed a clerk and committed suicide after a despairing midnight phone call to his ex-girlfriend, reporter Randa Phillips.

An interview with Cameron’s uncle--who happens to have been dead for three years, but Phillips doesn’t know this--sends her back to her native Georgia to warn the reclusive Jack that “the curse is real.” They fall in love even as Jack feels his own sanity crumbling.

*

The demon, who has a mordant sense of humor, begins to show his hand. Meanwhile, Kinney, Jack’s all-too-fallible would-be exorcist, is talking in dreams with a Christ who is “warm but demanding as hell” and wears a flannel shirt.

A disclaimer: I have always felt that the evils of the world were sufficient in themselves and had no need to titillate myself by believing in demons (or vampires or space aliens). “Dark Debts” doesn’t make me change my mind. But Hall clearly takes this stuff seriously, has researched it and wrestled with the problem of evil in a Christian context--to the novel’s benefit.

The confrontation between potent malice and shaky faith is the most deeply felt and thought-out part of the story. In contrast are the formulaic touches that persist in showing through the fabric, as hard to ignore as those mysterious stains on the Shroud of Turin.

A tale as grim as “Dark Debts” surely needs comic relief, but too much of Hall’s dialogue displays a smirky sitcom wit.

And must everyone in the book be such Beautiful People?

Phillips, for example, at first seems to be just another low-paid scribbler on an alternative L.A. paper, but it turns out she has a “world-class figure,” an honors degree from “a college that prided itself on an impossible curriculum and a high suicide rate,” and a trust fund that lets her jet back East when destiny calls.

Jack Landry, a morose ex-convict and day laborer in his late 40s, has “perfect teeth,” looks like a movie star when he’s dressed up, and knows his way around luxury hotels, having worked in one once.

Even the guy in the flannel shirt fills it out nicely. For all his tough-love philosophy and unsettling aloofness, he has the blond hair and blue eyes of the Jesus in a picture on a Sunday-school wall--a heavenly hunk.