Murphy's Law Rules Vegas Bachelor Party in 'The Hangover'

Four friends travel to the gaming and carousing center of Las Vegas to give one of them a bachelor party on the eve of his wedding. What could possibly go wrong? As it turns out, just about everything does in a bawdy but very funny new film. Here's a look at The Hangover.

It's a road trip from Los Angeles to Las Vegas where best friends Stu and Phil along with future brother-in-law Alan plan to give Doug a rousing celebration just before he gets married.

It starts with the promise of fun and maybe even a bit of debauchery as they raise their glasses in a toast to the groom; but things are quite different the next morning. Their hotel suite looks like a tornado has ripped through it: broken furniture, torn curtains, holes in the wall and, for some reason, a chicken cackling and strutting about.

The three of them have no recollection whatsoever of the night before. Three of them? One is missing: the groom!

So now they have to retrace their steps, figure out what happened, find Doug and get him back home in time for the wedding, which is to take place that afternoon.

The ensemble cast of The Hangover features Justin Bartha as the misplaced groom and he says the comedy gets more and more outrageous as the friends learn about their wild-and-crazy night.

"There are definitely moments where you say 'this is shocking' and hilarious. This movie has a ton of those moments. It really does," Bartha says."There's a naked gangster that jumps out of a trunk onto someone's shoulders, beats them up and then runs away. I've never seen that in a movie …and I always have wanted to."

Ed Helms plays Stu who is a dentist so when he wakes up with a tooth missing he knows strange things must have gone on.

"A lot of things in the script were initially not explained and it's so much fun to portray the aftermath of this night and let the audience try to put pieces together with our guys as they move through the story," says Helms.

Among those pieces: Stu, who has a fiancée back in Los Angeles, has somehow married a cheerful exotic dancer named Jade played by Heather Graham.

"I actually thought it was fun to play such a colorful character and not just the 'sidekick' to the guys," Graham says. "I got to be this quirky character on my own and I made up my own back-story where I was a spiritual new age stripper just trying to share my sexuality with the world for the great goal of spirituality."

Bradley Cooper is Phil, the groom Doug's best friend and organizer of the bachelor party, which turns into a frantic mystery.

"That's the cool part of the movie," Cooper says. "If you like these three guys together and you care about what they're doing then you're going to go on the ride because you are in the exact same head space that the guys are in.

Rounding out the quartet is Zach Galifanakis as the groom's quirky future brother-in-law. A veteran improvisational comic, Galifanakis says some of the funniest scenes were not originally in the script.

"The outline of the movie was a very good blueprint, but any comedy director wants you to improvise and we did improvise a lot," he says. "There were a lot of lines that were fine in the script but things change when you shoot so you kind of go with the flow."

The director is Todd Phillips, whose previous films include the hit Old School - another 'buddy' comedy - and he says it was important to make the real Las Vegas environment part of "The Hangover" story.

"I just think comedy plays so much better when it plays against reality, so I always want it feel as organic as possible. If we're going to shoot in Caesars Palace [hotel] I'd like to cut inside and be in the Caesars lobby," Phillips says. "I'd like to be shooting at Caesars pool or their valet (parking area). All of that stuff is really important."

The Hangover also features a cameo by boxer Mike Tyson along with several prominent Las Vegas celebrities.