Behind the scenes of Avengers: Infinity War as new heroes unite — and others will end 

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The sky is a raging sea of iron gray storm clouds, and a faraway rumble rolls across the countryside like something gigantic colliding with the other side of Earth.

Thor and Captain America are standing on an African savanna beside a sparkling river, back-to-back for the first time in ages, each reunited with his old friend while wielding new weapons. Cap’s red-white-and-blue shield is gone, replaced by a pair of vibranium gauntlets (courtesy of Black Panther’s genius little sister, Shuri), while Thor swings a mystical ax known as Stormbreaker, a supersized upgrade from his demolished hammer, Mjolnir.

The skyline of Wakanda’s capital city stands in the distance, and Cap and Thor are among hundreds of tribal warriors from throughout the nation, gathered at the river’s edge to join the heroes in facing down a horde of synthetic-alien demons known as the Outriders.

(out April 27), and it’s not just about saving the world this time — Earth’s mightiest heroes, and some from much farther away, are trying to save the entire universe from a cosmic tyrant who’d like to kill off half of it.

Right now, the cast and crew of the biggest team-up in superhero-movie history have a real-world problem to confront. The river is fake, of course. It was dug out of this grassy horse field near Atlanta, and giant pumps at either end recirculate the water as needed. The savanna is a lot closer to Savannah, Georgia, than any plains of Africa. The fictional skyscrapers of Wakanda are represented for now by a greenscreen, and the Outrider attackers are actors in speckled motion-capture suits.

But the looming rainstorm happens to be real. Chris Hemsworth lowers his battle-ax and looks off into the distance, wondering aloud if he saw lightning. The God of Thunder is in a race against his own superpower.

If the production is close enough to see a flash, union rules ­stipulate that everyone has to take shelter for 30 minutes. They might not have that long before the downpour begins, so directors Anthony and Joe Russo are hurrying to get their shots while supervising multiple camera units on different scenes.

For instance, on the other side of the river, Sebastian Stan’s Bucky Barnes, the former Winter Soldier now known to his Wakandan friends as “White Wolf,” is laying waste to Outriders while Rocket — in the form of Sean Gunn, wielding a puppet stand-in — distracts him with some offers he can easily refuse.

“How much for the gun?” the furry dealmaker asks, admiring the firepower clutched by Bucky’s mechanical limb.

“Okay, how much for the arm? The arm?” Rocket persists. (He has a weird thing about prosthetics.)

is not just in assembling what appears to be the entire roster of Marvel’s cinematic superheroes in common cause; it’s in pairing the oddest of couples.

Even Hemsworth and Chris Evans, on the other side of the water, are watching video playback and conspiring to make Thor and Cap’s reunion just a little bit weirder as the dropships of Thanos strike the ground.

Evans suggests that when they bump into each other, they do what friends often do after being apart for a while: assess each other’s haircuts. In some ways, they’ve swapped styles. Thor has gotten a clean-cut trim, while Cap is sporting the ragged locks and beard.

“I’ll be like, ‘Short hair now? Good choice,’” Evans says, while miming a right hook against an invisible Outrider.

“And I’ll go, ‘Yours too. The beard. Very ­rugged,’” Hemsworth says. They’re still workshopping it as they go back in front of the cameras. But before they can complete their takes, lightning crackles nearby, followed by curtains of stinging rain that send the whole production stampeding for cover. EW’s Day 1 on the set comes to an abrupt and muddy end.

Maybe that exchange between Cap and Thor will make it in, maybe it won’t. The thing about

is, you can’t really be sure what will survive.

This movie is a culmination, a punctuation mark on 10 years of superhero storytelling that changed the way movies are made. Kevin Feige, the president of Marvel Studios and the mastermind behind its interlocked universe of films (now totaling 19, with more on the way), says he wanted

and next year’s still-untitled follow-up, which was shot at the same time, to also be pioneering.

“The notion of an ending, the notion of a finale, became very intriguing to us, in large part because you don’t see it that often in this particular genre,” he says. That doesn’t mean there won’t be any more movies. Disney has already announced at least 10 more films set in the Marvel Cinematic Universe (or 11, counting the sequel to

, which will be released by Sony but is now part of the interlinked story).

Feige is aware the only thing that could kill the franchise is complacency, if they don’t keep evolving and engaging a new generation of moviegoers with a new generation of movies. The real danger is lack of surprise.

Some heroes are just getting started: Chadwick Boseman’s Black Panther, Benedict Cumberbatch’s Doctor Strange, Tom Holland’s Spider-Man, and Brie Larson’s Captain Marvel, who isn’t expected to be in

, although her first film, due next year and set in the 1990s, is shooting now. Other heroes have had multi-film arcs, with actors who have hinted they’re ready to move on, or at least step back. One of them is Robert Downey Jr., whose charisma in the first chapter, 2008’s

“Clearly, Kevin is, in addition to everything else, an excellent, almost clairvoyant troubleshooter,” Downey tells EW. “I think the trouble is the endlessness.”

Between Feige and the Russos, Downey says the cast feels their alter egos are in capable hands. “We’re going to pull out the stops, and stop exploring conventions, and look to do stuff where we go, ‘Oh, but if we do that, that’s very, very definitive.’ Well, great, let’s get definitive for a change!” Downey says. “We’re like a family now. Ten years later, we’re hanging out and having lunch, and kind of wondering when the draft is going to come in. Which one of us bites it and when?”

’s screenwriters, Christopher Markus and Stephen McFeely, who co-wrote all three

movies. Some heroes may simply get to ride off into the sunset. Others may sacrifice themselves or fall in battle. “It’s safe to say we will say farewell to people,” McFeely promises.

So, some things must end. And the idea of clearing away some to make way for others is the plan of the villain — Thanos, a godlike galactic warlord played via performance capture by Josh Brolin. Ever since the first Avengers film featured his smirking purple face as a post-credit surprise, he has been built up throughout this series as the ultimate tyrant.

“He’s from a planet called Titan that’s no longer inhabited because of things that he thought he could help prevent, and he was not allowed to do that,” Feige says. “What he feared most happened, and the planet and everybody on it basically went extinct. He vowed not to let that happen again. He thinks he sees the universe going down the tubes. He thinks he sees life expanding outward unchecked. That will bring ruin, he believes, to the universe and to that life.”

Since Thanos is a glass-half-full guy, he sees his mission as saving half the universe. But to do that, he wants to kill off the other half.

“That’s either genius or horrific, depending on your point of view, and most of our point of views say it’s pretty horrific,” Feige says.

The man also loves his work. “All the kind of grabbing-of-the-moon because of the gems, and all …?” the actor says with a deep laugh. “That’s the fun stuff.”

Intergalactic genocide is no easy task, so to accomplish his goal, Thanos needs his legion of genetically engineered Outriders to help him acquire the six Infinity Stones.

When combined into a single mystical gauntlet, those gems will allow him to bend time, space, energy, and the laws of physics and reality. The stones have been the plot drivers of many Marvel movies, but only one has yet to be revealed—the orange Soul Stone.

“He’s on a hunt,” Joe Russo says. “We’re using a bit of a ’90s heist genre component. Thanos is on a smash-and-grab, and everybody’s trying to catch up the whole movie.”

Doctor Strange has the green Time Stone, Benicio del Toro’s the Collector has the red Reality Stone, and the intergalactic police force Nova Corps has the purple Power Stone, while Tom Hiddleston’s Loki has snatched the blue Space Stone. The yellow Mind Stone is embedded in the forehead of Paul Bettany’s Vision and was the key component to bringing him to life. It’s doubtful he can survive long without it.

took us into the woods on the same equestrian ranch, doubling as Wakandan jungle. Cap, Black Panther, Scarlett Johansson’s Black Widow, and Mark Ruffalo’s Hulk are protecting an ailing Vision, who collapses in agony as Thanos and his gauntlet of space gems draws near.

“Vision is a living MacGuffin,” Anthony Russo says. “Obviously, that raises the stakes because Vision’s life is in danger, and his life is in conflict with Thanos’ goals, so something’s got to give.”

Stalking the heroes through the overgrowth is Proxima Midnight, one of the warriors Thanos kidnapped when they were young to train as bloodthirsty lieutenants, just as he did with his estranged “children” Gamora (Zoe Saldana) and Nebula (Karen Gillan).

“Cap makes the decision to bring [Vision] here to Wakanda,” Anthony Russo says. “Earth is making its last stand to keep the stone from Thanos. It’s the best place to make your last stand.”

An important part of the lore of Wakanda is that the fictional African nation is so powerful it has never been successfully invaded. That’s no longer the case, but Black Panther and his people are doing their best to push Thanos’ army back out again.

“It’s never been conquered, but that doesn’t mean it hasn’t been challenged,” Boseman says.

This is all new for Okoye, Danai Gurira’s head of the Dora Milaje, Wakanda’s special forces. She just got used to opening up to ­foreigners; now she’s fighting alongside talking raccoons and aliens. “Change is scary,” the actress says. “But I think the learning curve is to become a citizen of the world versus a citizen of Wakanda.”

Still, T’Challa and Okoye welcome Cap, Vision, and the others as friends, as allies, to their homeland. As we saw at the end of

, the new king wants his powerful country to stand up for more than itself. The whole universe seems like a good place to start.

“They trust each other,” Boseman says of Panther and Cap. The actor points to his gift of claw shields from Shuri (Letitia Wright,) forged from Wakanda’s sacred natural resource. “His shield was already made from vibranium anyway. So it’s just an extension of what he already had. This time, actually giving it to him, as opposed to…” Boseman shrugs. The materials for the old shield were likely taken, not offered. “Me actually giving it to him is a testament to our relationship and trust.”

Trust is all some of the heroes have left. Johansson says Black Widow, who has always been on the cynical side of the good-guy spectrum, now has faith in only a small circle of friends. “I think it’s been a dark time. I wouldn’t say that my character has been particularly hopeful, but I think she’s hardened even more than she probably was before,” the actress says.

As with Black Panther, Cap is one of the only people Natasha Romanoff still trusts. “It’s always felt like Natasha uses her cynicism as a defense mechanism. She weaponizes it for survival,” Evans says, sitting with Johansson during a break. “I think Steve is a little newly calloused in the ways of the world. But Natasha is always going to be a couple steps ahead of him in terms of experience and knowledge. They’ve leaned on each other for different reasons. It’s reinforced the friendship.”

Somehow, despite their differences, they get along. It’s a lot easier between two people than 50, but that’s what the characters of this story will have to accomplish.

Most superhero origins follow a similar pattern. The good guy discovers a power, then figures out how to wield it for good. In

, after so many movies about heroes bickering with each other, the superpower they discover is solidarity.

“They’re fractured at the start of the movie,” Joe Russo says. “It was always the intent, in a larger arc, to split the Avengers up before the greatest threat that they’ve ever seen. Thanos is a virtually indestructible character, which makes him an extremely difficult character to fight.”

Anthony Russo adds: “In the face of this, it’s like, ‘Can you overcome the divisions that have developed between you to face a common cause?’ That’s really the question.”

Beside the woodland set is a lake, where a falcon can often be spotted pulling fish out of the mirrored water.

That’s should be Falcon with a capital F: Anthony Mackie’s mechanical-winged hero.

During breaks between shots, while other actors are meticulously watching out for snakes and ticks, he takes out a rod and reel and ventures down to the water’s edge to catch dinner. (I hinted at this on Twitter back on June 2, now here’s what that actually meant.)

Sometimes words mean more than they seem.

— Anthony Breznican (@Breznican) March 8, 2018

Mackie says his character isn’t comfortable in Wakanda. He actually doesn’t trust a lot of the other heroes, and has a grudge against Iron Man and Black Panther from the events of

. “Everybody went their separate ways. Hulk, Iron Man, everybody separated and figured out how not to get caught or investigated,” Mackie says.

Now, as he puts it, Marvel’s heroes are trying to “get the band back together.” As he talks, he gets a tug on his line and reels in a largemouth bass, a suitable meal. But after removing his own hook, Mackie looks into the fish with concern. He asks for the pliers on his tackle box.

This fish has been caught before. There’s another hook from a broken line embedded in its throat. Mackie tries to remove it but can’t.

“Lucky I caught him. I should just keep him and cook him,” the actor says. Instead he lowers the fish back to the water, swishes it, and lets the tough old creature swim free.

“If it ain’t killed him yet, it ain’t gonna kill him,” Mackie says.

For Marvel’s superheroes, that’s the best they can hope for, too.