Anne Fontaine’s Adore used to be called Two Mothers because it concerns a set of best friends, Lil (Naomi Watts) and Roz (Robin Wright Penn), who have affairs with each other’s grown sons. This is indeed the premise of the Lonely Island and Justin Timberlake’s video “Mother Lover,” but instead of going for a comedic angle on this strange setup, Miss Fontaine attempts to make an edgy drama, though it never comes off as anything more than absurd.

Based on Doris Lessing’s novel The Grandmothers, Adore is set in New South Wales, Australia, in an idyllic beachtown where Lil and Roz live in neighboring sun-kissed houses bordering the blue. Lil is widowed and lives alone with her son Ian (Xavier Samuel), while Roz conducts a similarly unassuming and pleasurable life with her husband Harold (Ben Mendelsohn) and son Tom (James Frecheville), both theater directors. The movie sets up the exposition nicely by framing the two central women as lifelong besties (people in town even speculate that they’re in a lesbian relationship), but when Zeke goes off to Sydney for a job at a university, the loneliness and the boozed up fine dining allow each single mother to sneak into the house of the other and conduct illicit couplings with their nubile sons.

Much of the drama’s potential, the premise and implied discomfort notwithstanding, doesn’t track out after the romances heat up and the cameras continue rolling. The script by Christopher Hampton (Oscar-winner for Dangerous Liaisons) is so overtly melodramatic as to make the movie not only exceedingly unlikely but laughable, an overdose of soap opera enthusiasm that even includes a perfunctory slap-each-other’s-faces scene (when Roz gets upset at Ian). Ms. Wright and Ms. Penn are both fine actresses, and Messrs. Samuel and Frecheville, the oft-shirtless Aussie newcomers playing their sons, are stolid additions, but none of the character interactions muster enough realism to go beyond the level of sickly TV drama.

Miss Fontaine, a former actress and model, means for Adore to transcend the tawdry and popular by casting a distaff veneer on the absurdity. This she does by forming her two main characters as Mothers instead of Fathers and hence continuing the line of her vaguely feminist oeuvre. Adore comes right after the lush Coco Before Chanel, which Fontaine both wrote and directed, and its focus on the influential fashion designer (played by Audrey Tatou) reflects Miss Fontaine’s proclivity for strong and beautiful female leads. Adore is no exception, and its ubiquitous bleached blonde vacation scenes prove that Ms. Wright and Ms. Watts can indeed straddle the line between mother, a traditionally unglamorous screen role, and diva, a persona of charisma and allure. (Despite their middle age, the two show no signs of diminishing sex appeal.) Without a believable script, however, I never got the feeling that Roz and Ian were actually mother and son, or that there were any familial relationships at all going beyond the skin deep, however tanned. Flanked by their Hollister-esque sons and floating on a large dock in the sea, Ms. Wright and Ms. Watts leave the viewers with images of visually pleasing seaside excursions, and nothing else of note.

Movies with risque premises — Louis Malle’s Murmur of the Heart, a portrait of an incestuous relationship comes to mind — have succeeded at shocking audiences by finding the pain, awkwardness and emotion that can arise out of ‘extreme’ relationships. But such efforts are derailed by a flippant attitude towards realism; like a hyped bar with ultimately disappointing service, they entice the customer and then deliver vacuity. In this case, that emptiness is of hedonistic melodrama, captured in the movie’s final image of an illustratively vacant crane shot — a spiral down onto the languorous leads on a sea deck — and  proving with radical absurdity that Adore had said nothing radical.