Avengers: Endgame picks up twenty-three days after Thanos used the Infinity Gauntlet to disintegrate half of all life in the universe. Carol Danvers heads out into deep space to rescue Tony Stark and Nebula, and bring them back to Earth.
There, they reunite with the surviving Avengers: Bruce Banner, Steve Rogers, Thor, Natasha Romanoff, James Rhodes, and Rocket, who discovers Thanos’ whereabouts. They set out to take back the Infinity Stones, and use them to reverse the disintegrations. However, Thanos has already destroyed them to prevent anyone from doing that very thing. Thor is a bit pissed, and he decapitates Thanos.
Five years pass, and Scott Lang finally escapes from the quantum realm. He heads over to the big Avengers compound, where he tells Romanoff and Rogers that only five hours passed while he was trapped there. They theorize that the quantum realm allows time travel. So they track down Tony Stark to help them retrieve the Stones from the past, and reverse Thanos’ actions in the present.
However, Stark is now content to raise his daughter, Morgan, with his wife Pepper Potts, and he says no. When he sees a picture of himself with Peter Parker, he starts to reminisce a bit, and changes his mind. He goes to Banner, who by now has merged his intelligence with the Hulk’s strength, and the two build a time machine.
Banner, playing Captain Obvious, states that changing the past does not affect their present. It only creates a new branch of alternate realities. He and Rocket head over to Norway, where the Asgardian refugees now live at New Asgard, to recruit Thor to the cause. However, they find him overweight, out of shape, and drunk from depression in failing to stop Thanos. Romanoff heads to Tokyo to find Clint Barton who is now a vigilante following the disintegration of his family.
Banner, Lang, Rogers, and Stark travel to the Sanctum Sanctorum in New York City, 2012. There, Tony convinces the Ancient One to give him the Time Stone. The film cuts to Stark Tower, where Rogers retrieves the Mind Stone. However, Stark and Lang are unable to steal the Space Stone; allowing the 2012 version of Loki to escape with it.
Rogers and Stark next travel back to S.H.I.E.L.D. headquarters, 1970. Stark takes an earlier version of the Space Stone, and briefly encounters his father, Howard. At the same time, Rogers steals several Pym Particles from Hank Pym to return to the present. (Rogers will definitely be estranged from Pym for that.)
Meanwhile, Rocket and Fat Thor travel to Asgard, 2013 to get the Reality Stone from Jane Foster. While there, Thor retrieves his hammer, Mjolnir, and is elated to find out that he’s still worthy to wield it.
Nebula and Rhodes travel to Morag, 2014, and steal the Power Stone before Peter Quill does. Rhodes returns to the present with it, but Nebula winds up incapacitated when her cybernetic implants link with those of her past self. It’s through this connection that the 2014 Thanos learns he will succeed in his plan, and also of the Avengers’ attempts to undo his dirty work.
He captures 2019 Nebula, and then sends 2014 Nebula to the present in her place. Barton and Romanoff travel to Vormir, 2014, where once again, the Soul Stone’s keeper, the Red Skull, reveals it can only be acquired through sacrificing someone they love. Romanoff sacrifices herself because Barton has a family, and she only has the Avengers. Barton obtains the Soul Stone and returns to Earth quite distraught.
Everyone returns to the present where they reunite. They place the Stones into Stark’s homemade gauntlet. Banner volunteers to wield the gauntlet and bring everyone back that disappeared in the Decimation since believes he’s best suited to withstand both the radiation poisoning and the immense pain the Stones bring on.
He succeeds, but 2014 Thanos immediately arrives to Earth thanks to 2014 Nebula’s help. The quantum portal is destroyed in the process. 2014 Thanos and his warship reduces the Avengers’ compound to rubble.
This splits the team up, and the gauntlet falls to Barton’s protection. 2019 Nebula kills 2014 Nebula when she tries to get the Infinity Stones from Barton. At the same time, Rogers, Thor, and Stark take on Thanos. By this time, Thanos decides to use the Infinity Stones to destroy the current universe, and then create a new one in his vision.
The three take on Thanos one by one, with Rogers even being worthy enough to wield Mjolnor. Unfortunately, Thanos defeats each one of them. At this time, T’Challa appears, along with all of the Avengers Banner brought back, and they launch an all out assault on Thanos and his army.
During this mighty battle for it all, Stark reunites with Parker, and Quill reunites with a past version of Gamora. Thanos takes on a number of Avengers for the Infinity Stones. Suddenly, Captain Marvel reappears, and takes down Thanos’s ship while fighting for control of the gauntlet too. Stark takes the Infinity Stones from Thanos’ hand with his own, and uses them to turn Thanos and his entire army into dust.
“I am Iron Man,” he says as he dies from overexposure to the Stones while Parker and Potts console him.
With the battle over, The Avengers hold a funeral for Stark. His original arc reactor floats out on the lake next to his house. Barton and Wanda Maximoff rejoice that Romanoff and Vision would be proud of their victory over Thanos.
Thor coronates Valkyrie as the new Queen of Asgard while he joins the Guardians of the Galaxy to find his true purpose now that he’s free of the burden of royalty and the leadership associated with it. Barton returns home to his family. Parker returns to school, and reunites with his BFF, Ned.
Rogers is chosen to return the stones, and Thor’s hammer, to their original time lines in the past. However, he doesn’t return to the present. Instead, he chooses to live the rest of his life in the past with Carter. He reappears to Sam Wilson and Bucky Barnes as an old man in the present day where he passes his shield and the mantle of Captain America on to Wilson.
A brief flashback shows Rogers and Carter finally sharing the dance they never got to have in their living room; finally happy.
For a post credit scene, you will need to return to the past films yourself to watch their post credit scenes. You will find none here.