The premise of Adore, the new film from director Anne Fontaine, adapted from Doris Lessing's novella The Grandmothers, promises titillation, a dark flouting of taboo: Robin Wright and Naomi Watts play two childhood best friends who start sleeping with each other's teenage sons. Those boys, played by James Frecheville and Xavier Samuel, are shaggy, sensitive surfers, toned and tan and frequently shirtless. Watts and Wright are both blonde and lithe, regal but lo-fi beauties. So there's a lot to look at as these pretty people indulge their forbidden passions. But once the initial guilty rush has passed, Adore doesn't give the audience much. The film is withholding and distant, never quite articulating why any of this is happening.

Maybe that's because the four central characters have been dulled into a stupor by their dreamlike surroundings. Wright's Roz and Watts's Lil live on a dramatic, verdant stretch of coastline in New South Wales, both in well-appointed homes filled with expensive furniture. Lil's husband is dead and Roz's is mostly off in Sydney, so they are alone in this paradise, save of course for their strapping sons. Both mothers have jobs — Lil at a yacht design company, Roz at a gallery in town — but we mostly see them laid out on the beach, or on a floating wooden raft, then returning to Roz's house for wine and music. It's all very lovely, the four of them comfortable and blissed-out, everything soft and easy. Fontaine succeeds at seducing us with all this lush and laid-back beauty, and even though we knew she was going to destroy it, when the first transgression occurs — Lil's son Ian (Samuel) makes a move on Roz in the still of the night, she accepts — we still feel the shock of paradise lost, of a terrible flaw suddenly marring this perfect picture.

But Fontaine doesn't take that initial jolt of energy and do anything with it. Instead she keeps things loose and languid. When Roz and Lil find out what the other has done, they simply shrug their shoulders and push on, the film jumping ahead two years to when the foursome has cozily coupled off and formed bonds beyond the sexual. Of course the outside world does eventually intrude — Roz's son Tom moves to Sydney to direct a play (the character is never very credible as a theater type) and meets someone his own age — and anger and resentment flare up, but Fontaine only glances at all this stuff. We don't really know who any of these characters are; they begin to resemble dolls being pressed together to simulate something wicked.

Deeper motivations and meaning are teased at but then ignored. In one scene, Roz says that her husband is threatened by her friendship with Lil, and Lil responds with shock, saying "Does he think we're lezzos?" In another scene, the two friends pretend to be a couple to get a persistent would-be suitor away from Lil. There are interesting ideas there, a potential examination of the blurriness of intense friendships, the border between platonic and sexual love fading the closer you get to it. In that vein Roz and Lil are using Ian and Tom as proxies, as avatars for the one they really want to be with. If only the film explored that startling, unseemly idea instead of gliding along to standard melodrama. (The movie could also address the whiffs of incest-y closeness that these mother/son pairs give off, especially Lil and Ian. But that's far too intense subject matter for this decidedly breezy movie.)

Fontaine at least cast her film well. Wright is one of the most captivating film actresses of her generation, and even in vaguely shlocky fare like this she brims with wisdom, with a thoughtfulness that carries with it an oddly appealing sadness. She knows something we don't and we're ever eager to find out what it is. Watts has a little less to do here, but she plays well off of Wright, the two credibly creating the shorthand language of a friendship, elaborate communication through mere gesture and expression. Samuel and Frecheville are both intriguing up-and-comers, and Adore does allow them their moments; they're not simply studs to be manhandled, as they easily could have been. The invaluable Ben Mendelsohn also does nice, understated work as Roz's slightly estranged husband.

I just wish all these talented people had found themselves in a movie that was more interested in its own ideas, that took time to investigate or consider rather than fluttering through the typical motions of lust, love, jealousy, etc. With one of the sauciest, most potentially dangerous premises of the fall movie season, Adore could have truly unsettled and intrigued. But instead it is simply coy, blowing us a kiss before disappearing into the shimmering, empty sea.