The official website for The Avengers: Endgame has been updated with the film’s official plot synopsis, which per the movie’s marketing doesn’t offer much:
The grave course of events set in motion by Thanos that wiped out half the universe and fractured the Avengers ranks compels the remaining Avengers to take one final stand in Marvel Studios’ grand conclusion to twenty-two films, “Avengers: Endgame.”
The synopsis is similar to another description that has been floating around:
After the devastating events of Avengers: Infinity War, the universe is in ruins due to the efforts of the Mad Titan, Thanos. With the help of remaining allies, the Avengers must assemble once more in order to undo Thanos’ actions and restore order to the universe once and for all, no matter what consequences may be in store.
What remains to be seen is just how the Avengers go about taking their final stand as Thanos still has all six Infinity Stones, but what is questioned is if they can be used in unison again, as the end of Infinity War showed a damaged Infinity Gauntlet (Thanos used the Space Stone to port out). It’s guessed a new Gauntlet would need to be made, which was created by Peter Dinklage’s Eitri the Dwarf.
The Avengers also happen to have their own cosmic-powered Captain Marvel this time around whose powers originate from the Space Stone, the Tesseract, so quite possibly that could be a big clue as to how to defeat Thanos.
Another potential clue comes from the fact that there are six original Avengers and there happens to be six Infinity Stones. That might play into things somehow as well.
Regarding marketing for The Avengers: Endgame, the footage hasn’t revealed much, which, IMO, is a good thing and will make the movie all the better once it’s released.
The Avengers: Endgame has an April 26, 2019 release directed by Joe and Anthony Russo.