When last we left Thor, at the end of Thor: Ragnarok, he, Loki, the Hulk, Heimdall and the bulk of the Asgardian civilian population had conducted a Homeworld Evacuation aboard a large starship called the Statesman, with a Bittersweet Ending as Asgard itself was destroyed but Thor had accepted his place as their king. However, this film starts with a Happy Ending Override as the Statesman is attacked and crippled by the Sanctuary II, Thanos's personal dreadnought. Thanos's MO is to slaughter half the civilian population he finds, and he does so here, but he has a second goal: he is also after the Infinity Stones, Green Rocks of immense power. (They're not all green.) He alraedy has the purple Power Stone, last seen on Xandar (Guardians of the Galaxy (2014)). Even worse, Thanos is no pushover: even when Loki tricks him into letting his guard down, allowing the Hulk to get the drop on him, Thanos wins the one-on-one slugfest. It's a slaughter, overall; the Statesman is destroyed, and Hulk only escapes because Heimdall uses the Bifrost to send him to Earth. Heimdall pays for this with his life, and Loki is killed when he attempts another ambush. Meanwhile, Thanos gets the blue Space Stone from the Tesseract and travels away with his Quirky Miniboss Squad, escaping the Statesman before its destruction. Thor is left with an exploding ship and his brother's corpse.
Bruce Banner crash-lands in Manhattan, in the Sanctum Sanctorum, and is discovered by Doctor Stephen Strange and Wong, overseers of the Sanctum, and gives them grave tidings; Thanos is coming.
- Dr. Strange: Who?
The opening credits roll.
Somewhere in Manhattan, Tony Stark confides to his fiancée Pepper Potts that he had a dream of the two of them raising a child together, one named after Pepper's eccentric uncle Morgan. Pepper doubts his commitment: he's still wearing his Iron Man armor, now in a compact form that uses nanotechnology to hide in his arc reactor housing.
Either way, she's right: Strange calls Tony for help, and Tony learns of the existential threat of Thanos, a Demicidal Maniac who plans to wipe out half of all life in the universe. He is coming to Earth because two of the Infinity Stones are here: the yellow Mind Stone lives on Vision's forehead and has powered the android since his creation during Avengers: Age of Ultron; and Strange, de facto Sorcerer Supreme, keeps the green Time Stone on his person at all times. Bruce, of course, wants to call the Avengers, but he hasn't been on Earth since Age of Ultron — in other words, he missed seeing how the Avengers split down the middle during Captain America: Civil War. Tony still has that burner phone with Steve's number, but hesitates over the rift that has opened between them.
Before he can overcome his reservations, two of Thanos's "children," Ebony Maw and Cull Obsidian, go on the attack, seeking out Strange and/or the Time Stone. The Hulk, for whatever reason, now refuses to come out to play, but Wong is still around, and Tony has his nanotech Iron Man suit that can flash-forge additional weapons. Additionally, the team has a Sixth Ranger: Peter Parker, who sees Maw's ship approach Manhattan, joins the fray as Spider-Man. While Wong succeeds in using portals to trap Cull Obsidian somewhere in the Antarctic, Ebony Maw succeeds at subduing, though not killing, Strange, and absconds with him into space.
The film immediately breaks into Four Lines, All Waiting:
- Tony and Peter attempt to break into Ebony Maw's ship and rescue Strange, thereby preventing Thanos from getting the Time Stone.
- Up in space, Thor has survived the destruction of his ship. He is happened upon by the Guardians of the Galaxy, who are attempting to respond to the Statesman's distress call. The Guardians must decide how to stop Thanos from obtaining the Reality Stone, which since being extracted from Jane Foster has gone on to the custody of the Collector on Knowhere, and the Soul Stone, whose location no one knows about.
- Down in Manhattan, Bruce has the burner phone Steve left with Tony. He attempts to get back in touch with the other half of the Avengers to keep Vision and/or the Mind Stone safe.
- Thor's time with the Guardians is short-lived; Peter Quill is a little too self-absorbed to see that, despite the Trauma Conga Line he himself has suffered, Thor's is rather worse. Thor, furnished with a bionic eye by Rocket, takes "the rabbit" and "the tree" with him to Nidavellir, an ancient Asgardian installation where, so he has heard, he can procure a weapon strong enough to defeat Thanos.
As the remaining Guardians head to Knowhere, Gamora is haunted by flashbacks of when Thanos reaped her planet and "adopted" her. She reveals that she actually knows where the Soul Stone is — a planet called Vormir — and is, currently, the only one who does. She makes Peter promise that he will kill her rather than allow her to be captured by Thanos, and the two seal their bond with a Big Damn Kiss.
In Scotland, Vision has begun receiving cryptic warnings through the Mind Stone. He has come to visit Wanda Maximoff, the Scarlet Witch: while he sided with Iron Man during the Civil War, she sided with Captain America, and yet the Star-Crossed Lovers have continued to explore their romantic attraction in secret. It's just as well: the other two members of Thanos's miniboss squad, Proxima Midnight and Corvus Glaive, show up to separate Vision from the Mind Stone. By and large, it's an even fight, with only one problem: Thanos's underlings got the drop on them, starting by stabbing Vision In the Back. In short, the Avengers are losing. The Cavalry comes in the form of... The Avengers: Steve Rogers, Sam "Falcon" Wilson and Natasha "Black Widow" Romanoff, who help fight the two aliens to a standstill. They bundle Wanda and Vision aboard their quinjet and set course for Avengers Compound, where Bruce has welcomed them back. There, they meet with James Rhodes, War Machine, who became a paraplegic during the Civil War... but Rhodes is a soldier through and through, understanding that the threat of Thanos is more important than old grudges. (He does get some deadpan snarks in when no one is looking.) Vision offers to have the Mind Stone destroyed, sacrificing himself to thwart Thanos's plan. Steve, however, shoots down the offer: "We don't trade lives." Instead, he suggests falling back on Wakanda, whose higher Technology Levels might give them the ability to remove the Mind Stone from Vision safely.
Knowhere is already a flaming wreck, but Gamora succeeds at using her familial bonds with Thanos to get close; she stabs him and kills him. Anti-Climax Boss? No, a fake-out: Thanos already got the Reality Stone and used it to fool Gamora. With that stone, he incapacitates both Drax and Mantis, and then takes Gamora captive. Quill tries to keep his promise, but, courtesy of Thanos, his blaster only shoots bubbles. Aboard Sanctuary II, Thanos then tortures Nebula until Gamora gives up the location of the Soul Stone.
As Nebula escapes captivity and instructs the Guardians to rendezvous on Thanos's homeworld of Titan, Peter and Tony fight their way through Maw's ship, sending Maw flying into the depths of space and rescuing Strange. Strange wants to head back to Earth, uncomfortable at the idea of essentially bringing Thanos the Time Stone, but Tony is sick of waiting for the enemy to come to them. Fighting Thanos on his home ground will be risky, but at least it'll be on their terms and away from any civilians. Strange relents, but makes it clear that if he has to put The Needs of the Many before Tony or Peter, he will let them die. Tony then officially inducts Peter into the Avengers, leaving the 16-year-old Kid Sidekick both elated and unnerved.
Thanos takes Gamora with him to Vormir, where they encounter the Soul Stone's keeper, the man once known as the Red Skull, transported to Vormir by the Space Stone for his crimes and forced to guard the Soul Stone, a treasure he can never possess. The Red Skull explains that there is a price to be paid to claim the Soul Stone; one must be willing to offer the life of the person they hold most dear in exchange for the Stone. Gamora believes Thanos's plan is doomed to fail, claiming that Thanos cares for nobody other than himself. When she sees Thanos weeping silently, however, she has a harrowing realization; Thanos truly did love her as a daughter, but worse still, he is willing to offer her life for the Stone. Gamora struggles to break free of Thanos's grasp, but to no avail; he tosses her to her death, and takes the Soul Stone.
Thor, Rocket and Groot arrive at Nidavellir, a series of giant Dyson rings oscillating a neutron star. There's a problem — the star is cold. On further investigation, they find the dwarf, Eitri, who explains that Thanos held the dwarves hostage to build the Infinity Gauntlet, promising mercy in return for their services. Because of Hela's usurpation of the Asgardian throne, the dwarves couldn't call for help and were forced to bend to the Titan's wishes. Unfortunately, Thanos killed all the dwarves anyway and encased Eitri's hands in metal. Thor tries to reason with the dwarf, pointing out that with his guidance, they can make a weapon powerful enough to kill Thanos — Stormbreaker. Thor uses his strength and Rocket's shuttle-pod to force the rings to spin again and the star opens up. The energy is filtered through the rings into the forge and the process begins, but Thor has no choice but to hold the gate open manually, taking the full brunt of the star, slowly burning to death. However, the results are undeniably effective: Eitri forges "Stormbreaker," a hammer-axe, with Groot binding the two heads together and growing the haft from his own self. Stormbreaker flies to Thor's hand when summoned, instantly healing him.
Iron Man, Doctor Strange and Spider-Man make an extremely rough landing on Titan. Within seconds, they're confronted by the Guardians, with a predictable Let's You and Him Fight erupting before they figure out they're on the same side. Tony and Quill bicker over who gets to make the plan, but this ends sharply when Strange emerges from a trance. He's just used the Time Stone to scan over 14 million timelines — and out of all those possibilities, they won exactly once.
Back on Earth, the Avengers meet with King T'Challa, the Black Panther. With Thanos's army converging on Wakanda, the Avengers hold the line as they try to buy time to allow T'Challa's sister, Shuri, to remove the Mind Stone. They are joined by Bucky Barnes, whom T'Challa pressed back into service, and Banner joins the fray using the Hulkbuster armor to compensate for his inability to summon the Hulk. Thor also arrives here (later in the battle), and the film narrows down to Two Lines, No Waiting:
- On Titan, Thanos's homeworld, the space-going half of the Avengers — Iron Man, Dr. Strange, Spider-Man and the four Guardians of the Galaxy — attempt a Decapitation Strike against the Mad Titan.
- At Wakanda, the other half of the Avengers — Captain America, Black Panther, Bruce Banner, Bucky Barnes, Sam Wilson and Natasha Romanoff, with Wanda hanging back as Vision's personal bodyguard, and the Border Tribe, Jabari Tribe and Dora Milaje to fill in as Red Shirts, attempt to Hold the Line as Thanos's miniboss squad try to get to the Mind Stone.
When Thanos arrives on Titan, he explains to Strange the reason behind his actions: Titan was once an idyllic planet, but Thanos worried that overpopulation would exhaust the world's limited resources. He made a proposal to cull the population by half to prevent this catastrophe, but was denied. Unfortunately, Thanos was right: Eventually, Titan fell into ruin and became a lifeless wasteland. Extrapolating that the resources of the universe were similarly finite, he sought the Infinity Stones to wipe out half of all life in existence, allowing the remaining half to go on living without fear of extinction.
By All Your Powers Combined, Half The Avengers are able to subdue Thanos, with Mantis attempting to use her empathic abilities to put him to sleep. But he still has a Berserk Button to push: when Quill questions him about Gamora, Nebula, who has only just arrived, admits that she has been Killed Off for Real. It's only one Spanner in the Works, but it's all Thanos needs: as Star-Lord Turns Red over the loss of his Love Interest, he disrupts the Avengers' careful control of the fight, and Thanos breaks free. The gloves come off, and Thanos throws all he has at Half The Avengers, incapacitating most of them and winnowing it down to a Duel Boss fight against Iron Man, whom he succeeds at stabbing through the torso. Seeing this, Strange gives Thanos the Time Stone in exchange for Tony's life. When Tony asks Strange why he would do that, Strange implies this is that one chance at victory he saw, and anything else is already off the table. "We're in the endgame now."
Back on Earth, things have been going back and forth. Wakanda's Deflector Shields are sufficient to keep most everyone out, but Thanos's forces have enough reserves that they can throw themselves at the shields, slowly burning holes in them with their corpses. However, the fight turns back in their favor when Thor arrives via the Bifrost and a Large Ham entrance: "BRING ME THANOS!! It gets even better when Wanda, seeing the fight turning against her allies, abandons her post at Shuri's side to even the odds. Of course, this was exactly what Proxima Midnight and Cull Obsidian were planning for: Vision is now exposed. The remaining three members of the Miniboss Squad converge on him... but Vision, despite being weakened, is still able to take them with the help of Captain America and the others.
But then Thanos arrives.
He has five of the six Infinity Stones. He's almost invincible. The Other Half Of The Avengers throw themselves at him, to no avail. Of course, they're not necessarily trying to defeat him: they're trying to Hold the Line as Wanda finally agrees that Vision's Heroic Suicide is the only way forward. With his consent, she uses her powers to destroy the Mind Stone entirely... taking Vision with it.
But Thanos has the Time Stone. He shrugs and rewinds the whole scene, and then pushes Wanda aside, liberating the Mind Stone for himself.
At last, Thanos has all six Infinity Stones. Thor finally arrives, blasting the Mad Titan with lightning before hurling Stormbreaker at Thanos, the blade slamming full into his chest. Reminding him of his prior vow of vengeance, he pushes the axe deeper to ensure his suffering. But it wasn't an Instant Death Stab. Thanos is still alive. "You should've gone for the head," he whispers... and then, with the Avengers powerless to stop him, raises his Gauntlet-clad hand and performs a Badass Fingersnap.
Thanos finds himself in some sort of elsewhere, speaking to the child Gamora was when he adopted her.
- Young Gamora: Did you do it?
Thanos: Yes.
Young Gamora: What did it cost?
Thanos: ...Everything.
Back in the real world, the Gauntlet is heavily damaged, and Thanos retreats. The Avengers look around themselves to try and figure out what the fingersnap did. The answer is, it kills half of all life in the universe: as they watch, their friends dissolve into ash: The Winter Soldier, T'Challa the Black Panther, Groot, the Scarlet Witch, the Falcon. On Titan, Nebula and Tony watch as Quill, Drax, Mantis and Dr. Strange crumble into dust. "Tony... there was no other way..." are Strange's last words. But the last hits hardest: Peter Parker, the 16-year-old high-school student, staggers into Tony's arms, already beginning to flake away.
- Mr. Stark... I don't feel so good... I don't... I don't know what's happening. I don't want to go. I don't want to go, sir. Please... Please, I don't want to go... I'm sorry...
Steve Rogers collapses to the ground and looks at the ashy horror around him. Thanos had won.
Thanos, on some a far-away planet, watches the sun set pensively as he feels a sense of relief now that his life's work is complete, and contentment with the knowledge that he was the only one in the universe with the will to do what was necessary.
In The Stinger, Nick Fury and Maria Hill are confused when the car in front of them abruptly crashes. Hill goes to check on the driver, only to find the car is empty. When a helicopter suddenly crashes into the side of a building, they realize something colossal just happened. Fury watches in horror as Hill fades away, then sprints back to his car and grabs a high-tech pager to send out a distress call, only to find himself disintegrating. "Oh, no. Motherf-..." Fury curses as he fades away.
His distress call, however, manages to go through. Its recipient: Captain Marvel.
Thanos will return.
