The Hangover Part III follows the further (mis)adventures of the Wolfpack. It begins when Alan's outlandish behavior drives his father to death (literally), and he doesn't appreciate the gravity of the whole thing. His family decides to send him to a place in Arizona where he can get help, and they ask his friends, Phil and Stu, to be there when they tell him and convince him to go.
Phil, Stu, Doug, and Alan drive to Arizona, but on the way, they're forced off the road and abducted. The man who abducted them tells them that he wants them to bring their frenemy, Mr. Chow, to him. Chow has gone underground, but it appears that he and Alan correspond with each other. The man takes Doug and tells them to find Chow and bring him to him.
Eventually, they contact Alan and go to get Chow, but he knows what they are doing. He agrees to let them bring him to the man, but first, they need to break into a house to get something Chow needs to appease the man. However, Chow double crosses them, and they end up in jail.