The Girl Next Door

Where most good films spend their time developing one clearly defined path — cold woman learns to love, sad man finds happiness, old miser becomes generous, etc. — “The Girl Next Door” undertakes several such threads. Characters develop and mature in several ways, all building on the central idea of a young protagonist finding his way in the world.

And yet at the same time, the movie is about a porn star who moves in next door to a horny teenage boy.

Such is the paradox that is “The Girl Next Door.” Its premise is pure sex-farce, but its themes are more introspective. It has, for all its audacious laughter, a wistful tone about it, defying romantic-comedy conventions to become a genuinely unusual coming-of-age story.

The star is Emile Hirsch, who plays Matthew, a high school senior who is student body president despite being only mildly popular. He looks younger and shorter than his fellow students (thanks to the Hollywood trick of casting 20-somethings in their roles, while Hirsch himself is 18), and feels unconfident around them. He associates primarily with two oversexed dorks named Eli (Chris Marquette) and Klitz (Paul Dano), not because he’s as bottom-rung as they are, but because he thinks he is.

Matthew is destined for Georgetown in the fall, but his plans there are not specific. He feels the angst of uncertainty, the sadness of not knowing how he fits into the world. And then he meets Danielle.

Danielle (Elisha Cuthbert) is the 20-ish girl who moves in next door to do two weeks’ worth of housesitting for her aunt. She is gorgeous, and she is not averse to changing clothes with the blinds open. For reasons Matthew cannot fathom, Danielle likes him. His confidence is boosted, and he begins to hold his own among his peers.

That could be the end of the movie, plot-wise, but we’re only 20 minutes into it. Thanks to Eli’s extensive knowledge of pornography, Matthew learns that Danielle is a porn star. Since Matthew’s primary contact with women has been through porn, we now see his awkward idiocy as his feelings toward her change from affection to lust, leading to another incident of lesson-learning.

There’s almost a feminist vibe to the film, in places, as the effect of pornography on women is discussed, and especially as it’s made clear that Danielle lacks the self-esteem to try any other profession. Her agent, the predictably but amusingly slimy Kelly (Timothy Olyphant), won’t let her out, and soon he and Matthew are butting heads over their contradictory wishes for Danielle’s future.

It all leads to The Big Dance, as it often does in teen films, only here a few of the boys have porn stars for dates, and they’re grabbing people off the dance floor to sneak off and do some amateur filmmaking. So, you know, it’s a little different.

The film is a joy to watch, often very funny, always engaging and consistently unpredictable. I kept thinking I knew where it was going, and then it would surprise me by changing directions. Technically, this jumping from one genre to another, and from one plot trajectory to another, could be considered a liability, a symptom of an unfocused screenplay, but I don’t care. It makes the film stand out among its peers. There’s nothing wrong with breaking the rules, as long as the result is entertaining.

That said, I do think the film, directed by Luke Greenfield (“The Animal”), suffers from some lapses of logic that do it harm. Matthew’s panic over the loss of some school fundraiser money is unlikely, given that the loss was entirely the bank’s fault, not his, and the very notion, subsequently raised, of a porn film’s plotline being copyrightable is absurd.

It was written by David T. Wagner, Brent Goldberg and Stuart Blumberg, the former two being the scribes responsible for “My Baby’s Daddy” and “National Lampoon’s Van Wilder.” “The Girl Next Door” has elements of those films — the sexual humor, the randy teens — but it infuses them with real characters and actual comedy.

Emile Hirsche has a very natural, vulnerable charm to him, and he is completely believable as a confused teenager. Elisha Cuthbert, who plays everyone’s favorite dumb girl on TV’s “24,” demonstrates here that, given something to do, she can do it.

I like these characters, because I like their flaws and foibles. And I like the film’s small touches, the throwaway jokes that are sometimes as funny as the big, blatant ones. It’s as raucous a comedy as, say, “Eurotrip” or “American Pie,” but it has the feel of something better, something truer.

B (1 hr., 45 min.; R, a lot of harsh profanity, a lot of nudity, some strong sexuality.)