Dear diary …

Marielle Heller’s The Diary of a Teenage Girl is a coming-of-age story endowed with sharp characterizations and uncommon amounts of emotional honesty. As an R-rated account of a teenage girl’s sexual and emotional awakening in the San Francisco of the 1970s, it is bold and frank, but never merely sensationalistic or prurient.

Based on Phoebe Gloeckner’s illustrated novel from 2002, Diary focuses on one Minnie Goetze (pert Bel Powley), a bright, lively and somewhat lonely high school kid who’s getting herself primed for sex, romance and whatever other pleasures and adventures seem to beckon in the world around her (friends, family, post-1960s in the Bay Area, etc.).

In some crucial ways, the film is also about Minnie’s liberated party-girl mother, Charlotte (Kristen Wiig), her estranged but not entirely absent father (Christopher Meloni) and Charlotte’s boyfriend, a semi-lackadaisical lothario named Monroe (Alexander Skarsgard). Wiig’s Charlotte, a reluctant adult at best, is both unwitting enabler and ambivalent role model to Minnie, and in the story’s most provocative component, they become temporary rivals in a distinctly unconventional way.

The latter is a key part of the fireworks emerging from the story’s most dramatic and confounding development—the wildfire sexual relationship between Minnie and Monroe. First love mixed with amour fou makes a certain “natural” sense, but add sex with a minor, a whiff or two of something close to incest, an intimate sense of willpower’s asymmetrical battles with the sex drive, etc., and you’ve got an extraordinarily potent set of moral and emotional quandaries in full view.

Heller deals with all that in admirably even-handed fashion. Her film gives a pungent sense of a particular era in a particular place, but it plays no blame games and avoids simplistic perspectives on all three of the central characters. If there’s any special pleading, it comes from the characters themselves, and Heller and the actors show us both the truths and the illusions in whatever the characters have to say.

Gloeckner’s book is a mix of printed prose and drawn comic-style panels, and Heller’s adaptation takes appropriately eclectic form via live-action drama with a mix of voice-over narration (from Minnie) and intermittent animation sequences (credited to Sara Gunnarsdóttir). But Heller’s version plays as a fully realized film, with its own sense of authentic originality.