“Unforgettable” lets the hated Katherine Heigl stop pretending she was ever going to be “America’s Sweetheart” and wear her resting bitch face with pride.

As a filthy-rich ex-wife hellbent on getting her husband and family back, she has the regal posture of the riding classes, born in designer clothes and perfect makeup. She combs her perfect hair, then combs her daughter’s  so obsessively that you just know she’s an upper crust psychopath.

“Now you’re perfect, just like Mommy!”

And we buy it. Boy do we buy it.

The movie may be nothing more than your standard love triangle, with its scheme-by-scheme, crime-by-crime set up for a third act cat fight, but Heigl and Rosario Dawson are well-matched foes, women willing to throw down and draw blood over the man they both love.

The guy? Well, generic chiseled hunk Geoff Stults (TV’s “Odd Couple”) doesn’t suggest “unforgettable” or “irresistible,” but that’s always where this sort of thriller loses points.

Dawson is Julia, an online story editor for a magazine, leaving that life behind for her new man. We’re told that she was a domestic abuse victim, and that her abuser’s been in jail and he’s about to get out.

She’s motivated to slip out of town and “start over.”

David (Stults) is a wealthy, successful something-or-other who’s starting a micro-brewery (little late for that) living just inland from those “Big Little Lies” richies. Julia fits right into his showplace house, with his darling shared-custody daughter.

Yeah, it’s like she’s living the ex-wife’s life. So when they meet, she offers reassurances.

“I get it,” she says.

“No, you couldn’t possibly.”

And any assurances that Tessa, the ex will “calm down” are, we know, a joke. She can’t calm down. She’s wrapped too tightly for that.

Things start to go wrong for Julia —  phone misplaced, a ring lost, a future step-daughter escaping into a carnival crowd.

And everywhere she turns in this enclave of wealth, they run into Tessa.

Undermined, isolated, suspected and accused, she is alarmed. She turns testy at Tessa. And it’s on.

“I hope I’m not interrupting.”

“Then why are you HERE?”

But there’s no mystery to this thriller, and little suspense. The entire story is framed in flashback, after a crime. We know who’s survived.

The cameras stalks Julia, but the editing isn’t above delivered the occasional cheap fright — a dark night, a shadow slipping by a window. But the script and producer-now-a-director Denise Di Novi (“The Sisterhood of the Traveling Pants” and TV’s “Beaches”) want to explain everything, spoon-feed it to us, to wholly give away motives and back story. When you meet Tessa’s mom (Cheryl Ladd), you understand all.

You give away the mystery, you make the movie lean too hard on its implausibilities. Well, we DO tend to keep WAY too much personal data on our cell-phones. Get into somebody’s phone, you get into their head.

There’s soap opera-styled over-sharing, and the picture is peopled with stock characters; the funny best-friend-from-work (comic actress Whitney Cummings) whom Julia confides in, the mother-whose-behavior-explains-her-daughter’s.

But Dawson makes us believe how overmatched Julia feels, and Heigl’s “Mommy Dearest meets Fatal Attraction” turn is real mustache-twirling villainy. What will she do to get back what was hers? What WON’T she do?

If this hits, and it could, we could see a whole new chapter in Heigl’s struggling, diva-damaged big screen career. No more frothy, ill-conceived romances, just scary Joan Crawford/Barbara Stanwyck/Bette Davis/Theresa Russell minxes, black widows and back-stabbers. She’s already the movie star America loves to hate? Why not get paid for it?

MPAA Rating: R for sexual content, violence, some language, and brief partial nudity

Cast: Katherine Heigl, Rosario Dawson, Geoff Stults, Cheryl Ladd

Credits:Directed by Denise Di Novi, script by Christina Hodson, David Leslie Johnson . A  Warner Brothers release.

Running time: 1:40