AVENGERS: INFINITY WAR

★★★ ½ out of 5

Cast: Everyone (Chris Hemsworth, Josh Brolin, Robert Downey Jr., etc.) Director: Anthony Russo, Joe Russo Duration: 2h29m

Count on Robert Downey Jr. as Tony Stark to sum up this two-and-a-half-hour monster Marvel movie in just 13 words: “He’s from space. He came here to steal a necklace from a wizard.”

“He” is an all-powerful bad guy with Josh Brolin’s voice and Washington’s Mount Rushmore chin who gets an even briefer introduction at the end of the opening scene, when news arrives on Earth in the form of what I’m going to call a Hulk-ogram. “Thanos is coming!”

Thanos wants the Infinity Stones, a sextet of MacGuffins that have been noisily coming together for the past 10 years and 18 films. The Time Stone is in a necklace and gives the wizard Doctor Strange (Benedict Cumberbatch) his powers. The Mind Stone sits plainly in the forehead of Vision (Paul Bettany). The Soul Stone is presumably somewhere in Motown. I’ll leave you to discover the others — unless Thanos gets to them first.

Rather than list the rest of the performers, it might be easier to say who’s not in the movie: Paul Rudd’s Ant-Man and Jeremy Renner as Hawkeye sit this one out. The cast is so sprawling that we’re an hour in before we’ve caught up with them all.

One of the very few newcomers is Peter Dinklage in what might be his biggest screen role yet. He plays a giant dwarf who has to help Thor forge a new weapon, after his last one got shattered in Ragnarok. (Hammer time!) His scene is one of a number of (thankfully) lighter moments spread through the picture. Another reminds us of Rocket’s fetish for prosthetic devices.

Christopher Markus and Stephen McFeely are the scribes behind the Captain America movies and return for this one, as do directors Anthony and Joe Russo. They do a remarkably good job of juggling actors and locations that span the Earth, the galaxy … and even Scotland.

And for once a villain’s quest is easy to understand, if not to root for. Thanos has clearly read Malthus’s 1798 Essay on the Principle of Population and decided that the only way to save the universe from ruin is to cut the number of residents in half. “They called me a madman,” he crows at one point, forgetting that “they” are usually right about such things.

So on the one hand we have a being willing to trade trillions of lives for greater prosperity for the survivors, and on the other a group ready to sacrifice their own lives to stop him. And there are sacrifices aplenty along the way — although it must be said that Loki’s back-from-the-dead performance in the last Thor movie makes me wonder if anyone in this universe ever truly perishes.

It’s also worth noting that with so many good guys spread out across so many fronts, there are endless opportunities for herecomes-the-cavalry moments, to the point where one ticked-off character asks why her rescuer was just off-screen for so long before swooping in to help at the last second.

And where previous Marvel outings have delighted in hero-on-hero matchups (Hulk v. Iron Man, Spider-Man v. Captain America, and the amusingly brief Black Widow v. Ant-Man), Infinity War puts all the good guys on the same side — well, except for a short misunderstanding when two teams show up to fight Thanos at the same time. In fact, one of the movie’s most touching moments is a pre-battle chat between, of all beings, Thor and Rocket Raccoon.

The ending is easily Marvel’s most shocking yet, so the less said the better. It doesn’t so much hang viewers from a cliff as drop them off and leave them in the dust below.

It’s a powerful final note, undercut by the understanding that the team is already deep into production on Untitled Avengers Sequel, due out next May.

If Infinity War was the Second World War, I’d go all Churchill and declare that this is not even the beginning of the end. But it is definitely the end of the beginning.