"The Pineapple Express" is something of a surprise. True, it has the familiar pleasures of a Judd Apatow concoction: fearless raunch, funny situations and a couple of clueless-but-lovable boobs fronting the action. Apatow cooked up the story — about a pair of stoners on the lam from murderous drug thugs — with Seth Rogen and his writing partner, Evan Goldberg, who then wrote the script together. Rogen gives his usual endearing performance as a career pothead (few actors can throw away a line with such shlubby élan), and James Franco, shedding his heartthrob persona like cumbersome skin, does a revelatory comedic turn as a dealer who's been huffing his own leafy wares for way too long. (He's the best reason to see the movie.)

Sounds good, no? The surprise is what a mess the picture turns into.

Rogen plays Dale Denton, a process server who spends his days smoking joints in his car between jobs dropping subpoenas and divorce notices on people. (He wears disguises to avoid spooking his targets before he can lay the papers on them, but this comic device is never developed, and quickly peters out.) Franco plays Dale's dealer, Saul Silver, a zone-out with the energetic presence of a sack of laundry. Saul has a vague ambition to someday be a civil engineer (another largely pointless plot point), and in his abundant spare time he's invented a "cross joint" — a crucifix-shaped doobie that provides a triple hit for the adventurous stoner. "This is what your grandchildren are gonna be smoking," Saul says, as proud as if he'd just completed the Chartres Cathedral.

Saul has the best weed in town, and the very best right now is a Hawaiian variety called Pineapple Express. (It's so good, he says, squinting through a curtain of reefer-cured hair, that "it's almost a shame to smoke it — it's like killin' a unicorn"). Dale buys a bunch of this awesome bud and takes it with him to his next job, serving papers on a man named Ted Jones (Gary Cole) — who, unbeknownst to Dale, is the local pot lord. Toking up outside the man's house, Dale raises his fuddled gaze to a big second-story window and witnesses Jones and a crooked cop named Carol (Rosie Perez) blowing away an Asian drug rival. Dale makes a chaotic getaway, but Jones finds the half-smoked joint he left behind and immediately IDs it as Pineapple Express — his own product. He dispatches a pair of bumbling thugs (Kevin Corrigan and Craig Robinson, the droll doorman in "Knocked Up") to lean on one of his midlevel dealers, a hapless buffoon named Red (the hilarious, on-a-roll Danny R. McBride). Red is Saul's supplier, and, weasel that he is, he quickly aims the thugs in Saul's direction.

From this point, the picture collapses into an unwieldy chase film — a conflicted hodgepodge of strained slapstick and puzzlingly bloody beatings and shootouts. There are some funny sequences — a mad punch-and-stumble through the woods, a destructathon car chase — but they can't seem to decide when to stop; and there's a blazing showdown at Ted's hydroponic pot barn that seems never to have contemplated the question. There's also a feeble subplot involving Dale's girlfriend, Angie (Amber Heard), who's still in high school. (The movie has no qualms about scoring laughs from a scene in which Dale and Saul peddle pot to some grade-school kids in order to raise getaway funds, but it's careful to inform us that Angie is 18, and thus legal, which mutes the joke of Dale's pathetic involvement with her. Could there still be lines that can't be crossed, even in an Apatow picture?)

Unhappily, director David Gordon Green has to take the fall for some of the movie's structural flaws. It was a bold move to hire Green, a longtime indie-cinema star rightly esteemed for such small, vibrant films as "All the Real Girls" and "Undertow," and one understands his desire for a long-delayed mainstream payday. But his inexperience with action is apparent — he drags it out too long and, thanks to the script he was handed, he's never able to find a coherent tone for the picture.

It may have been an intriguing idea to combine pot-fogged comedy with the chattering Uzis of the action genre, but it's not particularly rewarding here. It isn't endless explosions and flying bodies we want from this sort of movie. We want more stoned babble, more of Saul saying things like "The monkey's outta the bottle, man." We want that pure, ineffable whatever.

Don't miss Kurt Loder's review of "Bottle Shock," also new in theaters this week.

Don't miss Kurt Loder's review of "Bottle Shock" and "Elegy," also new in theaters this week.

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