THE HERO of C.D. Payne's classic young-adult novel Youth in Revolt—and the new Michael Cera-starring film of the same name—is Nick Twisp, a bright but bitter young teenager ("even John Wayne on a horse would look effeminate pronouncing that name," Payne writes). His parents are separated, hostile, and generally unfit; his best friend Lefty (Erik Knudsen) is so named because his "erect member takes a sudden and dramatic turn to the east about midway up the shaft"; and Nick himself is entirely and unremittingly obsessed with sex, despite meager prospects of ever actually having any.

When Nick meets the beautiful and brilliant Sheeni Saunders (Portia Doubleday), it's lust at first sight. Inspired by Sheeni's attraction to dashing French movie stars like Jean-Paul Belmondo, and determined to win Sheeni away from her handsome poet boyfriend, Nick creates an alter ego, Francois Dillinger, who coaxes Nick into living dangerously—stealing cars and making moves on the irresistible Sheeni.

Michael Cera is well cast here in a role he's never quite played: that of an honest-to-god nerd. Not a hip nerd, or a hilarious nerd, or an adorably awkward nerd, or any of the relatively recent cultural permutations of nerdiness, most of which can be found somewhere in Cera's back catalog. No, here Cera is exactly what genetics intended him to be: bitter, lonely, and sexually unviable. (He also gets a chance to demonstrate a little more range than usual as cool-as-nails Francois.)

But a lot happens in Payne's plotty, 499-page novel, and screenwriter Gustin Nash is undone by his efforts to cover as much ground as the book: There's car theft, cross dressing, a road trip to a girls' school, and more, all furthering Nick's increasingly desperate attempts to get Sheeni in the sack. The result is more muddled than madcap, and some of the film's best characters get short shrift (Zach Galifianakis is hilarious as Nick's mom's boyfriend, but he makes a too-brief appearance).

Nash's unquestioning respect for the novel does pay some dividends, however. Payne's writing is cerebral and smutty at the same time ("Lately I have become morbidly aware of my penis," notes Nick in the book), and much of the movie's dialogue is lifted directly from Payne's prose. The result is an unusually brainy teen movie—and not, mercifully, in a too-clever Juno sort of way. Youth in Revolt is brainy like the movie's bitter, over-bright protagonist, whose voice, despite the plot's increasingly labored convolutions, remains funny and surprisingly believable.