Directed by Todd Phillips
Rated R
(Two and one half stars)
At the Admiral through Oct. 8: 1:45 • 3:50 • 6:50 • 9

Since “The Hangover” is a comedy about a bachelor party that goes horribly wrong, it makes sense that the film’s best scene shows the immediate aftermath.

The camera slowly pans a Las Vegas hotel suite that has been transformed into a still life of debauchery. Lamps are broken, a chorus girl’s costume is draped over a dresser and the armchair is smoldering. On the floor, a bleary eyed Stu (Ed Helms) is trying to come to grips with the fact that he is face to face with a live chicken.

This may have been the wildest bachelor party ever but Stu and his buddies, Phil (Bradley Cooper) and Alan (Zach Galifianakis), have no idea because they can’t remember anything about it. Worse, they can’t recall what they did with the groom, Doug (Justin Bartha), who is nowhere to be found.

If these friends are going to get Doug home in time for his wedding they’re going to have to reconstruct last night’s timeline from the few clues left behind (starting with the hospital I.D. bracelet on Phil’s wrist and a baby in the closet).

“The Hangover” works best as a comedy of reverse engineering. Screenwriters Jon Lucas and Scott Moore keep throwing surprises at the hapless groomsmen and let the script catch up with an explanation later.

It’s a funny device and allows director Todd Phillips to set the stage with flourishes of visual humor: Our three heroes pushing a car with an angry tiger inside is a touch that would have pleased Buster Keaton and the photo album at a Las Vegas wedding chapel hints at why Stu can’t find the engagement ring he had been planning to give to his girlfriend back home.

But while Phillips and his writing team know how to set up a funny scene they can’t seem to get a handle on how to play it out. “The Hangover” is as flat in its dialogue as it is brilliant in its outline.

Phillips doesn’t have the comic timing for an extended scene. More importantly, he doesn’t know what to leave out. The giddy energy of “The Hangover” has a lot to do with the audience being as baffled as the actors yet too often the humor has the life explained right out of it.

In fact, if that scene of Stu, the chicken and the wrecked hotel suite had opened the film it might have had a chance at greatness, but Phillips has already given us 20 minutes of cliché-riddled back-story.

If only Phillips had the vision to whack this lifeless prologue, he could have accomplished two things. One is to ramp up the film’s pacing to force a little juice back into the humor—and trust the audience to keep up. The other is to give Heather Graham more screen time.

Whatever its other failings, “The Hangover” benefits from an inspired cast and Heather Graham is the best choice of the lot. She blends the dizzy charm of Goldie Hawn and Katharine Hepburn into her role as Stu’s unremembered love interest. The fact that she is so underutilized may be the biggest mistake that Phillips makes in this film.

Cooper, Helms and Galifianakis are left to shoulder the main weight of the story and they do good work with it. They generate a satisfying chemistry as they are forced to confront the answers to questions no one should ever have to ask: is it wise to feed “roofies” to a tiger and what is the downside to being featured on Mike Tyson’s home security system videotapes?

Todd Phillips has shown himself to be one of Hollywood’s wobblier directors and “The Hangover” is an exasperatingly uneven effort. But when it’s good, well, it’s very good.