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Three weeks after the snap, Captain Marvel rescues Tony Stark and Nebula, stranded in space. The remaining Avengers track Thanos to a remote planet, but he has already destroyed the Stones so no one can undo his work. Thor, enraged, cuts off his head. It's no victory at all.
Five years pass. Natasha tries to hold the team together, Steve runs support groups, Tony lives in the country with Pepper and their daughter, Morgan, Thor drowns himself in beer in New Asgard, and Clint, who lost his family, kills criminals around the world as Ronin. Then Scott Lang escapes the Quantum Realm. For him, only five hours went by. An idea takes shape: use the Quantum Realm to travel through time and grab the Stones before Thanos does. Tony cracks the math, and Banner, now merged with the Hulk, helps build the machine.
The time heist splits the team. In 2012 New York, Steve, Tony, Scott and Banner get the Time and Mind Stones, but that era's Loki escapes with the Tesseract. Tony and Steve go to 1970 for another Tesseract, and Tony gets to talk with his father, Howard. In 2013 Asgard, Thor and Rocket pull the Reality Stone out of Jane Foster, and Thor sees his mother again and gets Mjolnir back. On Morag in 2014, Nebula and Rhodey take the Power Stone. On Vormir, Natasha and Clint learn the Soul Stone's price and fight over who will make the sacrifice. Natasha wins and dies. But the 2014 Nebula figures everything out, and that era's Thanos learns the plan and sends his daughter to the present in place of the future Nebula.
In the present, Banner puts on a gauntlet with all six Stones, snaps and brings back everyone who vanished. Right then, the 2014 Nebula opens the way and the 2014 Thanos bombs the Avengers compound. Now he wants to wipe out the whole universe and build a new one. Thor, Tony and Steve take him on, and Steve even lifts Mjolnir, but Thanos brings in his army. Then portals open: Strange, Wakanda, Asgard, the Guardians and every hero who came back arrive for the final battle. Captain Marvel destroys Thanos's ship, but he still gets his hands on the gauntlet. He snaps, and nothing happens: Tony has stolen the Stones. Tony snaps, Thanos and his army turn to dust, and Tony dies.
After the funeral, Thor hands New Asgard to Valkyrie and leaves with the Guardians. Steve travels back to return the Stones, but stays in the past and lives his life with Peggy Carter. As an old man, he shows up in the present and gives his shield to Sam Wilson. What happened to the 2012 Loki who escaped with the Tesseract is left open.