This is actually a two-parter that loosely based on the 1991 graphic novel "The Infinity Gauntlet" where Thanos use the Infinity Gauntlet to wipe out half of life in the universe. Well in the film, the Avengers are still torn apart after the events of "Captain America: Civil War" while Thor & the Hulk were heading to Earth with the Asgardians after the events of "Thor: Ragnarok" when they ran into Thanos who's after the Infinity Stones. Anyway, it was actually split into three stories: Thor meet the Guardians of the Galaxy, Iron Man & Spider-Man meets Doctor Strange and Bruce Banner (who's having trouble transforming into the Hulk) reunites with the rest of the Avengers to warn them about Thanos. It also includes the romance between Scarlet Witch & Vision and the romance between Peter Quill & Gamora. The movie ends when Thanos got all the Infinity Stones and use the Infinity Gauntlet to turns Doctor Strange, Black Panther, Spider-Man, most of the Avengers & Guardians of the Galaxy into dust. It left a cliffhanger where Thanos sit on another planet and watch the sunset. Although it show a post-credit scene where Nick Fury & Maria Hill turns into dust but not before Fury sent a distress signal to contact Captain Marvel (who will be in "Avengers: Endgame").
"Avengers: Infinity War" is one of the best Marvel films of all time. I can't wait until "Avengers: Endgame" come out in theaters on April 26.