As the days draw closer to Avengers: Infinity War, fans of the Marvel Cinematic Universe will be keen on learning more about Thanos' mission to restore balance to the galaxy. To do this, though, he requires six Infinity Stones to power his Infinity Gauntlet so that he can reshape the cosmos in his own twisted way.
However, one of these artifacts is still unaccounted for, resulting in never-ending speculation over its whereabouts. With the revelation that the Soul Stone really isn't in Wakanda after all, in-canon theories suggesting it's potentially the most dangerous of all the stones, and the potential that it may not even appear in the third Avengers film, it remains anyone's guess when we'll finally see the powerful item.
That said, if it doesn't debut in Infinity War, there's one another film that could reveal its location, the flick that comes directly before Avengers 4 in 2019: Captain Marvel.
We know that Carol Danvers' origin story as Captain Marvel will be set in the '90s, involve Samuel L. Jackson's early days as Nick Fury, and have a cosmic slant as it's adapting at least portions of the Kree-Skrull War from the comics. The Skrulls (shape-shifting aliens who often want to colonize Earth as per 2008's comic event Secret Invasion) are of particular interest because of recent developments that link Danvers, as well as the Super-Skrull, to the Infinity Stones in Marvel's books.
In the comics, the Infinity Gems (as they were once called) were recently destroyed and are now resurfacing as the Infinity Stones, surely to establish some sort of synergy with the movies. Eventually, the Reality Stone was found by Danvers during her adventures in an alternate universe. It was also revealed that the Super Skrull is wielding the Time Stone after excavating it from the depths of Sakaar (which Hulk ruled in the Planet Hulk comics and which we saw in Thor: Ragnarok).
Now, while these two particular stones are already accounted for in the MCU (the Collector has the Reality Stone or Aether; Doctor Strange has the Mind Stone), there's nothing to prevent Marvel Studios from shifting things around a bit to use the Soul Stone as a surprise MacGuffin in Captain Marvel. After all, these Stones are sources of immense power, so it would make perfect sense to learn the Kree and the Skrulls went to war over the Soul Stone. A movie introducing that fact by way of pulling in Danvers, who comes to realize just how powerful it is and that it can't fall into the wrong hands, practically writes itself.
This would also provide a logical reason why the cosmic-powered superhero goes off the grid and why we've yet to see her make her debut in the MCU: she's far way safeguarding the item so that no one -- whether it be Thanos, other aliens or even Fury and S.H.I.E.L.D. -- can exploit it. As a result, Captain Marvel's eventual arrival on the scene in Avengers 4 would end up being organic, relevant and perhaps even one that'll level the playing field against those who want to conquer the universe, such as the Mad Titan himself.
Directed by Anna Boden and Ryan Fleck, Captain Marvel stars Brie Larson as Carol Danvers/Captain Marvel, Samuel L. Jackson as Nick Fury, Jude Law as Walter Lawson/Mar-Vell and Gemma Chan as Minn-Erva. The film is targeted for release on March 8, 2019.