The full story
Endgame opens in the immediate aftermath of the snap. Clint Barton watches his entire family dissolve into ash. Tony Stark drifts through space, starving, recording goodbye messages for Pepper. The remaining Avengers track Thanos to his farm, hoping to use the Stones to undo the snap, but he has already destroyed them. Thor decapitates him in a fit of rage. Everyone is still gone.
Five years pass.
The world has moved on. Half of all life is still gone. Steve runs support groups for survivors. Natasha coordinates global operations from Avengers HQ. Tony has retired, raising a daughter with Pepper. Thor has fallen into depression and substance abuse in New Asgard. Bruce has merged with Hulk, achieving balance as "Professor Hulk." Clint has become Ronin, executing criminals across the globe.
Then Scott Lang escapes the Quantum Realm. For him, only five hours passed. He brings an idea: the Quantum Realm could enable time travel. They could go back, collect the Infinity Stones from the past, and use them to bring everyone back.
Tony initially refuses—he has a daughter now and a life he would lose if they change the past. But the memory of Peter Parker gets to him, and he works through the night to crack the equation. He agrees to help.
The time heist involves multiple teams traveling to different points in history. New York 2012: Tony, Scott, Steve, and Bruce attempt to retrieve the Space, Mind, and Time Stones during the Battle of New York, but Loki escapes with the Tesseract. Tony and Steve go further back to 1970, where Tony retrieves the Tesseract and encounters his father. Asgard 2013: Thor retrieves the Aether and speaks with his mother. Vormir 2014: Natasha and Clint confront the reality that one of them must sacrifice themselves for the Soul Stone. Natasha chooses to die so Clint can live.
Morag 2014 goes wrong. Nebula's cybernetic implants sync with her past self's network. Past Thanos learns everything. He sends 2014 Nebula back disguised as present Nebula, and she opens a portal for his entire army.
But first, Bruce snaps everyone back. Five years of dust reverses. Trillions of lives restored.
Then Thanos's ship destroys Avengers HQ.
The final battle features the three original Avengers—Tony, Steve, and Thor—fighting Thanos together. Steve wields Mjolnir. Portals open, and everyone returns: T'Challa, Shuri, Okoye, the armies of Wakanda, Strange, Wong, the sorcerers, the Guardians, and Spider-Man. "Avengers... assemble."
Thanos obtains the gauntlet and prepares to snap again. Carol nearly stops him, but he uses the Power Stone to knock her away.
Tony makes the play. He grabs the Stones from the gauntlet, loads them into his own armor. "I am Iron Man." He snaps. Thanos's army dissolves. Thanos himself crumbles to dust.
Tony Stark dies in the arms of Pepper Potts, surrounded by the people he saved.
Steve returns the Stones to their proper timelines but does not come back to the present. He stayed in the past and lived the life he never had. Now an old man, he passes his shield to Sam Wilson.
Endgame concludes multiple character arcs. Tony Stark sacrifices his life for the universe. Steve Rogers finally gets to live a normal life. Natasha demonstrates her commitment to the Avengers through her sacrifice. Thor grapples with his sense of failure.