San Francisco, 1976. The 15-year-old strides through the city park as the sun’s rays rain down and time itself seems to have stopped. “I had sex today,” we hear in exultant voice-over. “Holy [expletive].”
That the speaker is named Minnie — not, say, Max — shouldn’t have to be the point of “The Diary of a Teenage Girl,” and that’s sort of why it is. Or would be if Marielle Heller’s raw, funny, truth-telling coming-of-age story — adapted from comic artist Phoebe Gloeckner’s 2002 graphic novel of the same name — weren’t so alive to the basic business of being young and alive, of having terrible doubts and making dreadful mistakes yet still coming out infinite and complete.
There’s a scene early on of Minnie standing naked before her bedroom mirror, cataloging her flaws and contemplating her strengths, that makes you realize how rarely American movies delve beneath the skins of young women without freaking out one way or the other. Minnie is played by the British actress Bel Powley, who’s 23 — breathe easy, now — but who is effortlessly convincing as a baby-faced teenager with a big, rebellious brain and a body she hasn’t yet learned to trust. The heroine’s voice-overs, delivered into the microphone of a Bell & Howell tape recorder in Minnie’s bedroom, are the movie’s motor. They’re proud and insecure, profanely comic, dripping with adolescent wisdom and self-absorption.
But, yes, Minnie’s sleeping with her mother’s boyfriend, and that is a problem even if it’s mid-1970s San Francisco and the grown-ups are acting “looser,” to use Minnie’s semi-approving term. The boyfriend, Monroe (Alexander Skarsgard), is a lanky dude with a Steven Weed mustache, hazy notions of starting a vitamin empire, and a weakness when it involves underage girls bluntly coming on to him. What’s shocking and refreshing about “Diary of a Teenage Girl” is that it judges all its characters equally and on their actions, refusing to moralize while still allowing Minnie to find her own moral compass. It’s a long process, appalling and touching and, at times, refreshingly raunchy. Heller acknowledges the double helix of desire — of body and soul — that drives her heroine. “Someone wants me,” Minnie marvels while the affair with Monroe is still fresh. “Someone wants to have sex. With me.”
The mother, Charlotte, is clueless and a little lost; she’s played by Kristen Wiig in a finely drawn performance of a woman bobbing on the seas of a hedonistic era. (Minnie’s father is long gone, and there’s an ex-stepfather in New York, a fussy academic played by Christopher Meloni.) As is true of Gloeckner’s novel, “Diary” is fairly ruthless about the ways a girl can see her mother as emblematic of everything wrong with the entire universe before flipping, without quite knowing how, into something closer to shared sisterhood. But Minnie has to learn her own lessons before she can pay attention to anyone else’s.
Those lessons are embedded in a movie that is of its time and that stands back from it. The cultural reference points feel dead on — “H. R. Pufnstuf” on TV, “Rocky Horror Picture Show” at the neighborhood theater, Heart’s “Dreamboat Annie” giving way to the harder riffs of Iggy Pop and Television’s “See No Evil” on the soundtrack. Minnie’s an artist grooving on underground comix and filling her notebooks with doodles derived from the work of Robert Crumb and Aline Kominsky-Crumb; the latter becomes a sort of brassy spirit guide for the girl, and “Diary” occasionally bursts into animated fantasias of a giant Minnie lurching through San Francisco like a hormonal Godzilla.
This is Heller’s first film, but she rarely puts a foot wrong. “The Diary of a Teenage Girl” is a breakthrough moment in the culture in that it depicts youthful female sexuality — oh, all right, lust — not just with the unapologetic frankness the boys usually get, but with an awareness of all the places a girl’s urges will take her, for worse and for better. And it celebrates those urges, their wildness and the ways that wildness can be tempered by experience and by art. As Charlotte tells her daughter in one of her more lucid moments, “You have a kind of power. You just don’t know it yet.” “Diary” is a kind of origin story for average American superheroines. It’s the tale of how Minnie becomes electric.