“There’s no falling in love like the falling in love with a child,” the protagonist of “Loverboy” declares more than once. Certainly for this single mom it’s true. Emily (Kyra Sedgwick) fell for her son before she even conceived him, and adores him so much she’ll use whatever means necessary – bribes, trickery, homeschooling – to keep him all to herself.

That same refrain anchored the original novel by Victoria Redel, a chilling monologue of maternal obsession. At one point, the book’s narrator serenely describes her attempts to get pregnant by offering herself to any seed-producing stranger with the right genes. “Of course I had no plan. Only the big plan to have a broth of the wondrous possible inside of me.”

To write a line like that with a straight face takes guts. Ms. Redel’s short, unsettling novel had them. The film doesn’t.

Not that the story has changed much. Emily’s beloved Paul (Dominic Scott Ray) is the product of a one-night stand, which is the way his mother, whose own parents paid her no mind whatsoever, always wanted it. Her inheritance allows her to raise him full-time in a cocoon of warm affection, and mother and son spend several years in their own little world, addressing each other as “Loverboy” and “Miss Milady.”

But as he gets older, Paul begins to sense that something is wrong. He asks about his dad, and wonders why he’s not in kindergarten like the other kids. When a friendly, handsome neighbor (Matt Dillon) presents himself as a potential father figure, Emily scoops up her Precious and skips town. But the community they join – and Paul himself, who desperately wants to make new friends – forces Emily to put him in school, at which point she really begins to come apart at the seams.

Unfortunately, the film doesn’t offer much of a character to unravel. Director Kevin Bacon and writer Hannah Shakespeare take Emily’s foray into genetic engineering, for example – which could have added a pungently primal dimension to her urge to procreate – and play it for laughs in an early montage sequence that makes her into a tart. (It’s possible that audiences see Ms. Sedgwick nude more often in the film’s first quarter hour than Ms. Sedgwick’s own children ever will.)

Emily is facilely stamped – by way of a back tattoo – as a free spirit, which really makes no sense. This story calls for a single-minded protagonist with no interest in humans other than the little one she made herself. A logical person might expect such a woman to be withdrawn or uptight, or very much both. But the filmmakers probably concluded that such a woman is, like, really boring. Why else does this over-devoted mom dress like an East Villager (knit cap, vintage jackets) and prance around the house in cute undies that show off her abs?

Beneath the silliness and classic rock soundtrack lurks a close study of female power, not to mention a sharp critique of first-wave feminism. But the film, wanting nothing to do with either, beats a hasty retreat into the light and trite, mutating into a banal ode to thinking outside the box.

While Emily’s pathological attachment to her son doesn’t exactly make her a menace to society, it does make her a terribly irresponsible mother. And yet the film wants us to think she’s got the right idea – if only her own mom and dad had given her some love, it seems to say, she could have been the perfect parent. But since her mom and dad are portrayed (by Marisa Tomei and Mr. Bacon) in regular flashback sequences as cartoonish lunkheads, it is impossible to take this idea seriously.

“Don’t let boys give you trouble,” Emily recalls a beautiful woman (Sandra Bullock) once telling her. “All you have to remember is that deep down, they’re all afraid of girls.” So why, instead of trying to dramatize this theme, does the film make its leading female so prone to pratfalls? Emily walks in on her infant son sucking another woman’s breast and falls flat on her face; when a neighbor chirps that little Paul will make lots of friends, she promptly throws up.

That woman might have been right about girls. But there’s certainly nothing to be scared of here.