A couple of absurdly attractive middle-aged suburbanites lie in bed at the end of a long day, playfully nibbling on one another, until the female half stops to wonder aloud if their teenage son is having sex. A mother enlists her son's help in shopping for a dress to wear to get the attention of the TV star with whom she hopes to have an affair. A 17-year-old girl gets her boy best friend friend high, blindfolds him,  and orders him to suckle her ample breasts.

It's not HBO, it's Thumbsucker, the new movie from artist/music video director Mike Mills, which ends an almost year-long festival lap by opening in select theaters tomorrow. It's a curious thing, this film; episodic yet rambling, by turns sex farce and existential soap. It covers no real new territory for a top-tier indie, and yet it's an extremely satisfying film to sit through, funny and bittersweet, and unexpectedly epic in its emotional range. It almost seems to play the flip side to Gregg Araki's fabulous film from earlier this year, Mysterious Skin. That was the story of suburban teenagers trying to figure out how to be sexual beings whilst hiding dark, terrible secrets; this is the story of suburban teenagers trying to figure out how to be sexual beings, when their desires alone feel like dark, terrible, secrets. It's not hard to turn tragedy into comedy; a stroke of the mundane is all it takes.

Lou Taylor Pucci plays Justin Cobb, a 17-year-old who can't seem to stop sucking his thumb. He locks himself in the school toilet on rough days, knees bowed, digit in mouth, eyes dripping with self-disgust. At home, Justin looks on in horror as mom Audrey (a fabulous Tilda Swinton) enters a contest to win a date with her favorite TV hearthrob (Benjamin Bratt) – and then eventually changes jobs in an apparent attempt to be near him. He's in love with what at first seems to be the most emotionally mature 17-year-old girl on the planet, a Greenpeace freak named Rebecca (Kelli Garner). His kid brother (Chase Offerle) taunts him for not yet having had sex ("I hear it's the softest thing ever"). He has Vincent D'Onofrio for a dad. You'd suck your thumb, too.

Keanu Reeves plays Dr. Perry Lyman, who we instantly recognize as what would happen if Ted Theodore Logan, his bogus journey behind him, had traded in Kiss for Enya and decided to become an orthodontist. Dr. Lyman sucessfully hypnotizes Justin into thinking his thumb tastes like echinacea. Now everytime he tries to suck it he gags, but instead of thanking his orthodontist, Justin turns hysterical without his crutch. He calls Dr. Lyman and begs him to reverse the process. When the doctor refuses, Justin gets angry, and gets arrested trying to get revenge. The next thing you know, Mr. Geary, Justin's debate coach (played by Vince Vaughn, who more and more seems like the best comedic actor of that whole gang he runs with, if not of his entire generation) is recommending Ritalin.

The elder Cobbs, wracked with working-class parental guilt, need to be coaxed into the pharmaceutical solution. Audrey, a nurse, is wary of a quick fix; D'Onofrio's Mike, already embarrassed of Justin's long hair and skinny frame and saliva-soaked appendage, doesn't need to see another sign of his son's weakness. But Justin begs to be medicated. He doesn't like the way he is; he's not the romantically self-destructive type. The only thing he could possible hate more than being the guy who sucks his thumb is being the guy who can't face a life without thumbsucking. He sees Ritalin as his only way out of an otherwise sick and sad fate.

It works. Overnight, Justin morphs from a touchy-feely hippie in love, to a hard-as-nails, debate star/world-class bullshitter. Pre-Ritalin, Justin had the look of a zoo animal starting to atrophy to its cage. But the drugs melt down Justin's every reservation, and he's the only one who isn't surprised to see a rock star emerge. Even Mr. Geary, whose own life is given an injection of sudden meaning by Justin's debate ass-kicking, starts to wonder if maybe his protege hasn't gone too far. "Are you learning anything?" he asks after Justin brutally vaniquishes another opponent. Without missing a beat, Justin fires back, "I'm learning how to win." More than that: he's learning how to fight.

It falls apart for him at some point, and on his long way down Justin reacquaints himself with Rebecca. The two launch into the kind of psychologically-loaded teenage sexcapade series that a lesser film would stretch out for its duration, but it's a subplot that might be too much for this one to handle. Garner is phenomenally sexy in a real-life-girl sort of way. She and Rachel McAdams, I think, represent a new trend in Hollywood beauty – 2006 will be the year of the Big-Eyed Brunette. Her presence in Thumbsucker is such an intoxicating and overwhelming one, both for Justin and for the film space, that in hindsight it's hard to reconcile the fact that through her Justin goes from master debater to strung-out sex slave in the span of about three minutes. There's no question that this line of the story makes for incredibly pleasurable viewing, but in its resolution it raises a pile of questions that seem at odds with the film's other goals. Or maybe it's just tough to watch such a pretty, innocent looking girl devolve into a manipulative slag. In fact, it actually hurts.

If thought of as a series and snapshots and vignettes, Thumbsucker adds up to fully satisfying portrait of one teenage year. Small gestures – sideways glances, the flick of a page, a second cigarette lit at the finish of the first – stack up to create towers. Pucci is so good that in the final scenes it truly feels like you've sat in on a year in his life, but it's the supporting cast that really makes Thumbsucker work. Keep an eye on D'Onofrio: impenetrable the whole film, he says one line towards the end that cracks the whole thing open like an egg. The true aims of the film, also a little distant up until that point, start to ooze out.  I defy anyone, at that point, not to get a little wrapped up in the goo.