The plot is unknown at this time.
Did You Know?
On February 11, 2017, Marvel released the first on-set footage from the first day of filming (January 27, 2017). The footage featured a first look at one of the sets from the movie, with Robert Downey, Jr. (Tony Stark, a.k.a. Iron Man), Tom Holland
(Peter Parker, a.k.a. Spider-Man), and Chris Pratt
(Peter Quill, a.k.a. Star-Lord) shown on-set. Kevin Feige confirmed the movies as the culmination of the entire series from its beginning, with the first Iron Man movie. Feige also confirmed that the Avengers were broken into two sects in Captain America: Civil War (2016), in order to set up Infinity War. Feige describes Thanos as "The biggest, best, and baddest villain that Marvel has ever had", and states that Thanos will reveal his reasons for hunting down the Infinity Stones. Concept art was also shown depicting Rocket Raccoon fighting alongside Thor, although it his still not been revealed how the Guardians will meet the Avengers. See more
[facing off with the Avengers
Fun isn't really something one considers when balancing the universe. But this does put a smile on my face.
Referenced in Honest Trailers: Iron Man