I recently learned from science—meaning The New York Times—that during the millennia

I recently learned from science—meaning The New York Times—that during the millennia it took us to domesticate wolves into dogs, our genome co-evolved in the process. These once-fierce killers took advantage of us, we took advantage of them, and now we’re curled up on the couch together, watching Ellen and eating peanut butter from the same spoon. How is that possible? And how is it possible for the four-man wolfpack of the Hangover franchise to have been tamed in only four short years?

How? The first problem with The Hangover Part III is that it wants to tell you how, with regular references and flashbacks to Parts I and II, which earned their R rating with unbridled debauchery, dude-bros gone wild, trying to reconstruct their misdeeds after drug-induced blackouts. They were killing brain cells to avoid their wives and fiancees, to escape the crushing, black-hole gravity of suburbs, kids, and carpools. Not anymore.

This new chapter takes almost 30 exposition-heavy minutes to get going, and its plot then amounts to very little. Mr. Chow (Ken Jeong) has busted out of a Thai prison. He’s stolen some gold from a baddie named Marshall (John Goodman). Marshall then takes Doug (Justin Bartha) hostage, forcing the other three members of the pack to find Chow—or Doug dies.

There’s problem number two: Nobody cares if Doug dies. He’s like Zeppo Marx, disposable. (Can you even remember, one paragraph later, who plays Doug?) If director Todd Phillips had wanted to do something shocking here, he should’ve killed Doug straight away, explaining nothing. But instead our heroes are eventually sent on two not-very-interesting exfiltration missions: 1) get the gold out of a Tijuana mansion, and 2) get Chow out of a Vegas hotel penthouse.

A thousand heist films have been here before, and Phillips is no student of cinema—he just quotes old movies, including his own. From Chow’s prison escape through the wolfpack’s two bungled B&E jobs, this Hangover is mainly a recycling effort. Even the final scene is a slo-mo reprise. That’s the cheapest way to write a script, so you can put your money into the cast: Bradley Cooper as Phil, Ed Helms as Stu, and Zach Galifianakis as Alan (the last unmarried lone wolf in the group).

Cooper, thanks to Silver Linings Playbook, has finally turned the corner onto the A-list. He doesn’t need this movie, apart from the money, and it shows. Galifianakis’ calculatingly grating, needy man-child could be interesting in a stand-up context, but he’s been neutered here, put in a XL-sized adult diaper. Due Date and The Campaign have done nothing to prove he has a future in Hollywood. Helms’ put-upon dentist has emerged as the franchise’s only plausible, rounded character: panicky, pessimistic, yet surprisingly compassionate even to “a cancer” like Chow. Alan is dumb enough to trust that manic id-demon, believing they’re friends. Stu knows better, yet still he loyally puts his finger in the shit-fan. Stu is the series’ conscience; and Helms, as in Cedar Rapids and Jeff, Who Lives at Home, shows his gift for compromised ethics, decency under duress. Now that The Office is over, I look forward to seeing more of him.

A few F-bombs aside, this final Hangover is so tame that Wallingford dads could comfortably take their Girl Scout troops to the matinees. It’s a disappointingly soft movie, like Chow’s penthouse orgy pad—not naughty at all. When Heather Graham’s hooker shows up again, Jade is a contented cul-de-sac mom whose surgeon husband is cool with her past. The wolfpack respects her like any other housewife at a polite garden party where Mr. Chow will never be invited. He has to stay outside, the only one left to howl at the moon.

bmiller@seattleweekly.com

THE HANGOVER PART III Opens Thurs., May 23 at Sundance Cinemas and other theaters. Rated R. 100 minutes.