Lately, Jane Fonda has been doing a lot of apologizing. She's sorry for being so cavalier during the Vietnam War. She's sorry for Ted Turner. She's sorry for the cosmetic surgeries and the bad mothering and the eating disorders. She recently put her sorrys in a memoir big enough to choke a T. Rex.
The only thing she's not apologizing for is her new film, "Monster-in-Law," the mediocre prenuptial comedy that she hijacks from Jennifer Lopez. And really, why should ol' J.Fo apologize when her performance is the best thing in it?
The movie lets Fonda -- who hasn't acted on film in 15 years -- skewer her usual seriousness. She's accepted a part that calls for her to choke, slap, poison, kick, lie, punch, curse, shriek, and be generally loathsome, all while looking more fabulous as the movie wears on. She's a riot.
She plays Viola Fields, a domineering Los Angeles TV host who has just been replaced by a woman a third her age. Her demotion pushes her over the edge and lands her in a ritzy mental facility, which she exits just in time to meet Charlie (Lopez), the new girlfriend of her doctor son, Kevin. He's played by Michael Vartan, who's merely a handsome piece of scenery.
Kevin and Charlie are in love, and right in front of his disgusted mother he asks Charlie to marry him. Desperate to destroy her son's relationship, Viola launches a one-woman shock-and-awe campaign designed to expose her future daughter-in-law as an impatient rube and unrepentant slut. Neither shoe fits. So Ms. Fields switches tactics, aiming to drive Charlie crazy by trying to plan the wedding and moving from her estate into Kevin and Charlie's house.
Viola is so relentless and deranged in her offensive to taint Charlie's reputation that you half-expect her to turn up photos of Charlie on the arm of Sean Combs or Ben Affleck.
But Charlie's past (and her credit report) is dirt-free, and part of the pleasure in watching Fonda lay into her younger opponent is waiting for Lopez to snap back. The truth is she bends more than snaps. Lopez is not a very dynamic screen presence, though she does appear to enjoy herself more than she has in any movie since "Out of Sight." Not that her work in "The Cell," "Enough," or "Maid in Manhattan" is particularly hard to top.
Charlie is a dog-walking, dress-making, feel-good bohemian, the sort of free-spirited dabbler that, once upon a time, Goldie Hawn might have played. Lopez takes a similarly chirpy tack to her character's self-defense. At one point, Charlie drugs Viola, and Lopez politely pumps her fist while Fonda is face-down in a plate of tripe. She seems afraid that we won't like her if she demonstrates a trace of meanness, and that insecurity inhibits her credibility as an actress. Lopez could learn from Fonda's film persona that not caring what people think about you is freeing.
The movie feels adapted from a piece of chick lit. It's not. But all the same, the screenwriter Anya Kochoff seems naively inspired by the modern-fantasy spirit of those books. Charlie's hippest accessory, for instance, is her gay buddy, Remy (Adam Scott).
Director Robert Luketic brings the same intermittent hilarity, deadly pacing, and uncertainty to "Monster-in-Law" that he did to "Legally Blonde." He desperately turns to wisecracking Wanda Sykes, who plays Viola's exasperated servant, for punch lines even when she's not that funny. Incidentally, Sykes is a black woman whose loyalty to such a narcissistic white lady is an outlandish throwback, to say the least.
But "Monster-in-Law" has a hard enough time justifying its antagonist's monstrosity. It's ridiculous that a woman like Viola, who has pictures of herself with Oprah Winfrey, Nelson Mandela, and the Dalai Lama, has to resort to face smacks and crocodile tears to get her way.
It's also insane that Fonda's first big part in so long is so grotesque. But by Hollywood standards, a movie carried with such gusto by a 67-year-old woman has to be considered a miracle. And I'm not sorry to say I enjoyed watching her do it.
Wesley Morris can be reached at wmorris@globe.com.