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Thanos (voiced by Josh Brolin) is ambitious on a grand scale. Already responsible for the genocide of millions, he’s ready to up his game as one of the most heinous wrongdoers in the universe. That means acquiring six stones that will make him omnipotent — and unstoppable.

Earth is an essential destination on Thanos’ itinerary. But rather than proceeding quietly, he takes the traditional route — which involves causing mass mayhem in New York and inevitably attracts the attention of superheroes. In this case, they include Doctor Strange (Benedict Cumberbatch), Iron Man (Robert Downey Jr.) and the Hulk (Mark Ruffalo), who are less than pleased that the city is once again on the verge of being reduced to rubble.

Also alerted to the threat of Thanos are Thor (Chris Hemsworth), who has a good reason for seeking revenge, and the Guardians of the Galaxy — one of whose members, Gamora (Zoe Saldana), has a longstanding link to the supervillain.

The battle for humanity’s survival finds its way to the African nation of Wakanda, where Black Panther (Chadwick Boseman) soon realizes that his warriors might not be up to the task of defeating Thanos, even with Captain America (Chris Evans) and Black Widow (Scarlett Johansson) on their side.

But they won’t go down without a fight.

“Avengers: Infinity War” is just what you’d expect from Marvel Studios: a comic-book flick that’s as thrilling and enthralling as it is pretentious and preposterous. The story is just an excuse for the action sequences, and the Marvel strategy remains intact: When in doubt, blow stuff up.

Working from a screenplay by Christopher Markus and Stephen McFeely, directing brothers Anthony and Joe Russo deliver a film that’s overlong and overstuffed but somehow avoids being a chore to watch.

In a cast that’s mostly called upon to look either surprised or terrified, Cumberbatch and Ruffalo are standouts.

Don’t be too upset by the ending of “Avengers: Infinity War.” A sequel — and reportedly the final film in the “Avengers” franchise — is scheduled to be released next year.

What “Avengers: Infinity War” • Three stars out of four • Run time 2:29 • Rating PG-13 • Content Violence, action, language and crude references

Calvin Wilson is theater critic for the St. Louis Post-Dispatch.