Mavis Gary (Charlize Theron) is, as the title implies, still a teenager at heart, a mental state that comes in handy when ghost authoring a series of novels aimed at teenage girls, and less so anywhere else. Following the announcement that the publisher is pulling the plug on the series, she's feeling a little lost until she receives an email from her high school flame Buddy Slade (Patrick Wilson), announcing the birth of his first child. Disturbed but strangely motivated, she packs her clothes and Pomeranian pup and heads back to her hometown, with a determination to rekindle their old relationship, and steal (or perhaps rescue) Buddy from the hell that married life must certainly be.

The trailers are quick to identify Mavis as "that girl you hated in high school," but Mavis isn't a boring, vindictive ice queen. She's genuinely delusional, unable to believe that Buddy (played with an almost gleeful, doofusy cluelessness by Wilson) might actually like his life in small-town America. Luckily, she runs into Matt (Patton Oswalt), another high school acquaintance who is more recognizable through his history ("you're the hate crime guy!" she gasps, upon seeing his cane) than any memory Mavis might have of actually speaking to him. As teenagers, the social hierarchy of high school naturally kept them apart (despite being locker neighbors), but as adults, they bond over alcohol and their shared willingness to drop pretense when speaking to one another: he tells her she's nuts, and she quickly reminds him of his own shortcomings (living with his sister, his permanent disfigurement stemming from the aforementioned hate crime, in which a group of jocks mistakenly assaulted him for being gay).

It's no wonder that people liked the script for Juno: it must've stood out like a fire alarm, what with every line of dialogue for the titular teenager and her best friend constructed like little mazes of pop culture from past and present, spiked with a healthy dose of snark. Yet, the best characters were the ones played by Jason Bateman and Jennifer Garner, whose crumbling marriage packed a resonant punch in the absence of artificial wordplay. Young Adult refines the formula further, finding a perfect line between unfettered and the bite Cody wants to give her characters through their words. Some lines, like the barbs Mavis and Matt throw at each other, are pretty straightforward, but the ones Cody gives to Mavis ("We can beat this thing together!") are especially cutting in the silent exposition they deliver about the speaker. Meanwhile, Reitman also ditches the calculation inherent in the cinematography of his previous picture Up in the Air (which, to be fair, fit that film just fine) for a naturalistic look that slightly emphasizes the aw-shucks simplicty of everything surrounding Mavis.

All of this transparency serves the lead performances by Theron and Oswalt, who are both rounded and real. Oswalt mostly does what he does best, cracking sharp observations about Mavis left and right, but when he's called upon to do more, his subtlety and simplicity are impressive -- other actors would have played certain notes of the role much louder, and it would not have worked. Theron does one better, maneuvering a tricky dramatic and comedic labyrinth without any intruding trace of vanity or ego. Like Oswalt, her most skillful trick is the way she keeps the elements of Mavis that are deeper and truer than her infatuation with Buddy muted in a way that feels honest, never overplaying her hand or allowing sympathy to congeal into pity. The whole trio -- Cody, Reitman, and Theron, with an assist from Oswalt and a one-scene home run from Collette Wolfe as Oswalt's sister -- allow the audience to understand Mavis, trust in the viewer to see who she is and why without accidentally weakening her. Most films hope the viewer sympathizes with their characters, but in trying to generate that bond, they pander to the audience's good nature, refusing to suggest a similarity someone might not like. Not every aspect of people, good or otherwise, is positive, and too many movies bend over backwards to turn their cartoon caricatures to heroes, who deep down are just like us. It's false. We all have our worst moments. When Mavis looks in the mirror, don't flinch.