By all rights, this film shouldn’t work. Even at two and-a-half hours, the 19th movie set within the ever-expanding Marvel Cinematic Universe wouldn’t seem to have the time necessary to service the more than two dozen characters that star in Avengers: Infinity War. But against all odds, nearly all of Marvel’s superheroes get a moment to shine as they team up to stop the biggest threat that the world—and the galaxy—has ever faced.

One corner of that galaxy was explored six months ago in New Zealand director Taika Waititi’s delightful Thor: Ragnarok, starring Australian hunk Chris Hemsworth. Picking up moments after the conclusion of the third adventure headlined by the God of Thunder, Infinity War wastes no time to alert us that we’re in for a much darker ride, beginning in the midst of action. Brothers Joe and Anthony Russo (directors of the past two Captain America pictures, The Winter Soldier and Civil War) drop viewers into a devastating attack on the transport ship that was housing Thor and the remnants of his civilization, whose mystical realm of Asgard was destroyed. As bad as that sounds, things get worse.

The attack on their vessel is perpetrated by the purple-skinned, golden-armored Thanos. Known by comic book aficionados as the Mad Titan, this towering figure has been teased a few times since debuting during the end credits of the first Avengers film six years ago. That’s a long buildup for the Big Bad to finally make a proper entrance, but he was worth the wait.

As portrayed in a superbly understated motion-capture performance by Josh Brolin, Thanos continues a welcome trend of strong villains who possess clearly understandable motivations in Marvel’s recent movies, beginning with Michael Keaton’s portrayal of the Vulture in last year’s Spider-Man: Homecoming. And similar to Michael B. Jordan’s Erik “Killmonger” Stevens in Marvel’s Black Panther, Brolin’s contemplative nemesis believes what he’s doing is right and just—even if his plan to bring balance to the universe requires him to indiscriminately wipe out half of all life. To execute his plan, he needs to acquire six Infinity Stones, ancient gems that, when installed on the golden gauntlet he wears on his left hand, will grant him unlimited power over time, space and reality itself.

In many ways, Thanos is the star of this film, occupying more screen time than most of the heroes, who have been paired off into unexpected and pleasurable groupings spanning five or six concurrent plotlines by Christopher Markus and Stephen McFeely. The screenwriting duo was just warming up with their script for Civil War, which built up to a 15-minute fight sequence that was fantastically well-choreographed and executed by the Russos. That hero-on-hero battle royale was one of the best that Marvel ever put on screen. Until now.

Not only have Markus, McFeely and the Russos topped that battle, but they’ve done so repeatedly, beginning with an early fight in Greenwich Village that finds young Peter Parker (Tom Holland) suiting up as Spider-Man to aid his mentor Tony Stark (Robert Downey Jr.), also known as Iron Man, who’s been recruited by Doctor Stephen Strange (Benedict Cumberbatch) to help fend off two members (Tom Vaughan-Lawlor and Terry Notary) of the Black Order, Thanos’ four henchmen.

Likewise, a quiet Scotland getaway for the artificially intelligent android Vision (Paul Bettany) and Wanda Maximoff (Elizabeth Olsen), also known as the Scarlet Witch, is interrupted when two more of the Black Order (Carrie Coon and Michael Shaw) ambush them. Nearly beaten, a few friends arrive just in time during one of the film’s numerous great entrances—both on Earth, where Black Panther’s Wakanda serves as the backdrop for a massive ground battle, and in space, where the Guardians of the Galaxy’s endearing weirdness is handled flawlessly by the creative team. The interaction between Peter Quill/Star-Lord (Chris Pratt) and Thor alone is worth the price of admission. In space, no one can hear you scream—but they certainly can hear you laugh.

And really, it’s the humor that holds everything together. It’s a key component that Marvel president and chief architect—Boston-born Kevin Feige—has threaded throughout a decade of interconnected films, beginning with 2008’s Iron Man. And the strong personalities of the performers are necessary in a picture like this, not only due to each character’s relatively limited amount of individual screen time, but also to lend gravity to the dark places that the film backs our heroes into.

Sure, your own Mind Stone may tell you that the events of this film can’t possibly be permanent, but the ending still manages to pack a wallop. Think of this as Marvel’s version of The Empire Strikes Back: a classical tragedy that will shake up the status quo. It’s a massive gamble that will leave you hungry for next year’s as-yet-untitled sequel. And like the next issue of your favorite comic, it can’t come soon enough. ◆

Avengers: Infinity War   ★★★ 1/2

Starring Robert Downey Jr., Chris Hemsworth, Mark Ruffalo, Chris Evans, Scarlett Johansson, Don Cheadle, Benedict Cumberbatch, Tom Holland, Chadwick Boseman, Zoe Saldana, Karen Gillan, Tom Hiddleston, Paul Bettany, Elizabeth Olsen, Anthony Mackie, Sebastian Stan, Idris Elba, Gwyneth Paltrow, Benicio Del Toro, Josh Brolin, Chris Pratt and Stan Lee. Written by Christopher Markus and Stephen McFeely, based on the comics by Stan Lee and Jack Kirby. Directed by Anthony and Joe Russo. At Assembly Row, Boston Common, Fenway, Seaport, South Bay and in the suburbs.