Associated Press

Zach Galifianakis (from left), Bradley Cooper and Ed Helms in a scene from "The Hangover."

Two days before his wedding, a Los Angeles guy named Doug (Justin Bartha) and three buddies pile into a borrowed Mercedes convertible and blast across the desert intent on a bachelor party they'll never forget: a night in Las Vegas free of wives, girlfriends, fiancees and other dampening influences.

When Doug's buddies awaken the next morning, they find their hotel suite exhaustively trashed, a live chicken clucking around the premises, diverse inflatable creatures in the hot tub, smoldering furniture, a whimpering baby in the closet and a hungry tiger in the bathroom.

What they don't find is Doug; the groom has gone alarmingly missing the day before his wedding.

As for the memories the party boys had hoped to create ... zip. Not one of the throbbingly hung-over dudes can recall a thing about the night before.

At this point, "The Hangover" turns into a sort of demented detective story as the hapless trio tries to reconstruct the lost evening in order to recover the absent groom and get him back to L.A. in time to say "I do."

Their clues? One of the three is wearing a hospital bracelet. Another is sporting an unsightly gap where one of his teeth used to be. And when they dispatch the parking valet for their car, he produces not the Mercedes but the police patrol car that they apparently liberated the night before.

By film's end, they will be gleefully Tasered by schoolchildren. They will revisit one of Vegas' famously cheesy wedding chapels and the pretty hooker who stars in that chapter of the story. They will meet Mike Tyson (playing himself) and discover that he sings really badly but still packs a wallop. And they will violently intersect with a sissified but lethal Asian gangster (hilariously played by Ken Jeong).

As bachelor-party movies go, this one is definitely outside the envelope. For one thing, there's no party, at least not one that anyone remembers. And the structure is unusual. The story begins at the end -- wedding preparations -- flashes backward to the memorable but unremembered debauchery, then bookends it by switching back to the present.

Credit writers Jon Lucas and Scott Moore for that, along with a skein of lines and images that almost always work. If Friday's first screening in one Roanoke theater is any guide, patrons can expect a continuous ripple of laughter accented by jumps in the mirth meter whenever something said or done onscreen scores a direct hit on the audience funnybone.

Credit director Todd Phillips for holding it all firmly together. And, perhaps above all, credit actors Ed Helms, Zach Galifianakis and Bradley Cooper for their spot-on portrayals of the groom's pals. Helms, who plays Andy on TV's "The Office," is the henpecked straight arrow who loses a tooth but gains his self-esteem. Cooper is the schoolteacher who yearns to goose his staid life and succeeds spectacularly in Sin City. And Galifianakis, in what could be a breakout performance for this gifted comic actor, is the bride's 90-proof weirdo brother.

Female roles are mostly inconsequential in "The Hangover," though it shouldn't be dismissed as just another guy film. Women who forgo it will deprive themselves of what promises to be one of the summer's sharpest comedies.

One more thing: The laughs don't end when the story does. Stick around for the ending credits.