Plot

Two years after the bachelor party in Las Vegas, Phil, Stu, Alan, and Doug jet to Thailand for Stu's wedding, but Stu's plan for subdued pre-wedding brunch goes seriously awry.

Stu is getting married, and along with Doug, Phil, and his soon-to-be brother-in-law Teddy, he regretfully invites Alan to Thailand for the wedding. After a quiet night on the beach drinking beer and toasting marshmallows by the campfire, Stu, Alan, and Phil wake up in a seedy apartment in Bangkok. Doug is back at the resort, but Teddy is missing, there's a monkey and a severed finger, Alan's head is shaved, Stu has a tattoo on his face, and they can't remember anything. The Wolf-Pack retrace their steps through strip clubs, tattoo parlors, and cocaine-dealing monkeys on the streets of Bangkok to try to find Teddy before the wedding.—napierslogs

Dentist Stu Price is getting ready to marry Lauren in Thailand and his best friends, Doug Billings, Phil Winnick, and Alan Garner travel there for the wedding. After the dinner party, Doug, Phil, and Alan invite Stu to drink beer around a beach bonfire with Lauren's teenage brother Teddy; Phil brings the beer and marshmallows. The next morning, Phil, Stu, and Alan have hangovers and can't recall the night before; their room is a shambles; Teddy is missing but a little monkey is in the room; Teddy's finger is in a glass of water, Alan's head is shaved, and Stu has a tattoo on his face. As the trio start trying to figure out what happened, they discover Mr. Chow on the floor under the carpet. They learn that they are in Bangkok, and Mr. Chow is about to explain everything about the night before--but insists on snorting cocaine first, which puts him out of commission and Phil, Stu, and Alan to unravel their crazy night themselves--and find Teddy.—Claudio Carvalho, Rio de Janeiro, Brazil

It seems that some people never learn. Only two short years after that fateful night in The Hangover (2009), the original Wolf Pack, Phil and Doug, along with the awkward fourth wheel, Alan, find themselves in exotic Thailand for Stu's wedding to charming Lauren. Next thing they know, the boys wake up in a seedy Bangkok hotel, and to make matters worse, there's no sign of Teddy, Lauren's brilliant 16-year-old brother. Of course, none of them can remember what has happened the night before. Now, apart from a severed ring finger, a tiny Capuchin monkey, and the team's nemesis, Leslie Chow, lying on the floor, the team is clueless. But, once more, time is against them, and before getting to Stu and Lauren's wedding ceremony on time, last night's survivors must first piece together the fragments of yesterday's trail of destruction through the underbelly of the city. Can the amnesiac band decode the missing hours before it is too late?—Nick Riganas

A group of friends again experience a wild bachelor party night, this time in Thailand where, like their previous escapades in Las Vegas, they can't remember much and try to piece together the night in order to find a group member who has disappeared.

Two years after their escapade in Las Vegas, Stu (Ed Helms), Phil (Bradley Cooper), Doug (Justin Bartha), and Alan (Zach Galifianakis) are traveling to Thailand to celebrate Stu's wedding to his fiance, Lauren (Jamie Chung). Much to Alan's dismay, they are joined by Lauren's younger brother, Teddy (Mason Lee), a prodigy and Pre-medical student at Stanford University. At the wedding reception, Lauren's father shows his disapproval of Stu by comparing him to rice porridge in his toast. At the end of the night, Stu hesitantly joins Phil, Doug, Alan and Teddy for a beer. Sitting at a campfire and roasting marshmallows, the group toast to Stu and Lauren's future happiness. Doug has traveled with his wife Tracy, who is the maid of honor for Lauren. Lauren's dad is proud of Teddy. Alan is acting like a jerk throughout the engagement party.

The following morning, Phil, Stu and Alan, along with gangster Leslie Chow (Ken Jeong) (whom Alan befriended after Las Vegas) and a chain-smoking Capuchin monkey, awaken in a dirty hotel room in Bangkok. Stu has a face tattoo, and Alan's head is completely shaven. However, they cannot find Teddy, only discovering his severed finger. Chow begins recalling the events of the prior night, but his heart stops after snorting a line of cocaine. Panicked, the trio dispose of Chow's body in an ice machine.

Through Doug (who left early the preceding night and is still at the resort where the wedding is to be held), they find out that Teddy is waiting in jail. The police had given Doug a call after finding Doug's number on the body of the prisoner. Upon arriving at the prison, they are given a handicapped elderly Buddhist monk, who has taken a vow of silence. The Monk somehow had all ID proofs of Teddy. The trio and the monk travel to a bar after finding a business card inside the Monk's pockets. The reach the bar only to see the entire neighborhood smoldering in ruins. They enter a nearby tattoo parlor, where they are told that they had started a fight in the club that escalated into a riot & that led to the fire in the bar. The tattooist shows them a video in which the guys have started a riot & the police arrives. Teddy gives his jacket to the Monk, who is on a wheelchair, & can't escape the advancing police. The Tattooist also tells them which monastery the monk belongs to & asks them to check there for Teddy.

The trio then return the monk to his Buddhist temple, where they are encouraged by the head monk to meditate to help remember past events. The head monk also reveals that the guys climbed over the walls of the monastery and kidnapped the monk, that's how the monk ended up in front of the white lion bar, where the riot happened & the police picked him up. Alan is able to recall a strip club that they had gone to. There, they learn that Stu had engaged in sex with a Katoey prostitute at the bar (with Stu being on the receiving end). Upon exiting, the trio are attacked by two Russian mobsters from whom they had apparently stolen the monkey, and when they take the monkey, they shoot Phil in the arm.

After Phil is treated at a clinic, Alan confesses that he had drugged some of the marshmallows from the previous night with muscle relaxants and ADHD medication in order to sedate Teddy but accidentally mixed up the bags. Stu attacks Alan leading them to notice an address and time point for a meeting written on Alan's stomach. The trio arrive at a luxurious hotel to find another gangster, Kingsley (Paul Giamatti), who demands Chow's bank account code and password by the next morning in exchange for Teddy.

Kingsley claims that he had invested a large amount of money with Chow & Chow was supposed to give him a share of the profits, which he didn't, so Kingsley took Teddy hostage. They return to the hotel to try to find Chow's password, only to discover that he is still alive. After Chow explains that he had hidden the code in the monkey's jacket, they steal the monkey back from the Russian mobsters through a violent car chase, during which the monkey is shot and injured. After taking the code and leaving the monkey at a veterinary clinic, the group return to Kingsley's hotel to complete the deal. Suddenly, Interpol agents appear and arrest Chow. Kingsley turns out to be an undercover agent, who tells the trio that the police have searched all day for Teddy but were unable to find him. He obviously has no clue where Teddy is.

Desperate and out of clues, Phil once again calls Doug's wife Tracy to inform her of their dilemma. Stu then has an epiphany and realizes that Teddy must have woken up in the middle of the night to get more ice for his severed finger (after the first bucket of ice had melted) but became trapped after the power went out while he was ascending. The trio rush back to the hotel and find Teddy in the elevator unharmed (albeit still missing a finger). The four use Chow's speedboat, the keys for which were in Teddy's pocket, to travel back to the wedding reception.

Arriving just as Lauren's father is about to cancel the wedding, Stu makes a defiant speech where he rejects being boring and instead states that he is in fact quite wild. Impressed by Stu's sudden display of authority and confidence, Lauren's father finally accepts him and gives the couple his blessing. After the wedding continues on, Alan presents Stu with a special gift at the post-reception dance: a musical guest performance by Mike Tyson.

Later at night as Phil, Stu, Alan, Doug, and Tyson reminisce about all of their crazy escapades, Teddy discovers that he had taken many pictures during the night on his mobile phone. Once again, the group agree to look at the pictures together once before erasing the evidence of their exploits.