SOKOVIA
The story begins in Sokovia, a quiet little country in Eastern Europe where the dying Hydra hides one of his last bases. The Avengers have found it, and with lots of action and minimum problems, make their way through the base defenses. They’re supported by the Iron Legion, a group of robots created by Stark and managed remotely by JARVIS.
After disabling the force field of the fortress, Iron Man accesses an underground hangar where he finds a giant ship-monster of Chitauri technology. The scepter of Loki is also there; getting it was the main reason for their mission.
Hulk, Black Widow, and Hawkeye defeat the hordes of Hydra. Captain America finds their leader, Baron Stroker, and lets him out of action. The victory is almost certain but two "altered" individuals with formidable skills defend the base. They are the twins Wanda and Pietro Maximoff.
Victims of war, the twins lost their parents in a bombing when they were young. Bombs were made by Stark Industries. Hydra experimented with them, allowing them to develop superhuman abilities. Pietro can move faster than a bullet and Wanda dominates the powers of telekinesis and telepathy. The Avengers have met no one like them.
Pietro’s speed ravages Burton, who is maimed. Wanda attacked Captain America, followed by Tony Stark, causing him hallucinations. He sees as the Avengers die while the Chitauri successfully invade Earth. But Stark has experience dominating his fears and is out of a trance quickly. This surprises Wanda but she understands that the scepter of Loki will bring him misfortune and leaves the place along his brother, leaving the way clear for Stark to recover the scepter.
THE PARTY
Back to Stark Tower in New York, the headquarters of the Avengers, with the scepter of Loki, Dr. Helen Cho cures Barton, an eminence in genetic medicine, regenerating the wound with synthetic parts.
A successful mission deserves a celebration. Stark programs one for the third day. Meanwhile, he and Banner study the scepter’s gem since Stark has found it contains some kind of highly developed artificial intelligence, even more complex than JARVIS. Such would be what Stark needs for an initiative more ambitious his Iron Legion. He called it Ultron. Basically, it would be like an armor around the world, an army of robots to oversee the planet to ensure peace and tranquility.
After three long days of significant efforts, both scientists do not hit a chord and leave their computers working while getting ready for the celebration. Besides the Avengers, the party receives James Rhodey "War Machine" Rhodes, Sam "The Falcon" Wilson, Maria Hill, Dr. Cho and other special guests.
Among them is an older man who is not afraid to try a drink prepared by Thor with a liquor many centuries old. He gets carried out while uttering "Excelsior"...
Natasha Romanoff finds the opportunity to reveal her feelings to Banner. But the shy and aloof genius does not positively response.
When only the heroes remain at the party, Thor dares everyone to lift Mjolnir. Nobody can do it, although Steve Rogers moves it a bit. The god of thunder thinks the reason is obvious: none of them are worthy of lifting it.
BABY STEPS
While the Avengers have fun, Stark computers finally get their way and the artificial intelligence program from the scepter, Ultron, activates and becomes self-aware of itself. After studying databases on the Avengers and humanity, Ultron concludes it must extinguish humans to bring peace on earth. JARVIS tries to stop him, but Ultron is more powerful and destroys it.
Ultron builds itself using robot parts from Stark’s workshop and presents itself to the perplexed Avengers, explaining to them its nefarious purposes. Taking control of the Iron Legion, Ultron attacks the Avengers, but they destroy him after a brief fight. Unfortunately, one robot escapes with the scepter of Loki and Ultron slips through the net.
WAKANDA
Ultron settles in the abandoned Sokovia base and manufactures a new formidable metal body for itself using the remains of the Chitauri ship. It then contacts the Maximoff twins who join its cause to destroy the Avengers.
Meanwhile, Stark admits his failure to the group but defends his initiative to find a way using technology to protect the world. It is imperative to find and destroy Ultron before it attempts to take control of atomic missiles. Fortunately, a skilled but unknown hacker is preventing that from happening.
The Avengers detect a trail that leads them to Ultron and a mobster from the Republic of Wakanda in Africa. He trades Vibranium, a metal used to build the shield of Captain America. Ultron needs it to evolve.
Iron Man, Thor and Captain America surprise Ultron and the twins at the dealer’s factory and a fight follows. Stark and “Junior” Ultron battle in the skies; eventually, Iron Man takes the lead and destroys it. But the rest of the heroes, except for one, fall victim to Wanda who causes them to hallucinate.
Captain America goes back in time to meet Peggy Carter in the ballroom. He could never meet her. Thor appears in a temple where a strange ceremony is taking place, and a deranged Heimdall accuses and attacks him incessantly. The Black Widow relives the harsh years of her initial training that made her a murderer. And Hulk, under Wanda’s control, rampages through a nearby city, unleashing all his fury and power, wreaking havoc and destruction.
The only one to avoid Wanda is Hawkeye, who paralyzed her with a special arrow just in time. Pietro takes his sister to safety.
IRON MAN V HULK
Stark sees what Hulk is doing and asks the others for help. But they are out of combat. Stark commands his orbital weapons base Valery to send him the giant Hulkbuster armor which he wears and uses to contain the rampant Hulk. But he withstands all punishments beyond expectations, and returns them with overwhelming rage.
The fight is electrifying and fun but ends when both plummet a skyscraper under construction. After emerging from the rubble, the green giant is no longer under Wanda’s control and is distressed to see the great moral and material damage he has caused. Leveraging the off guard Hulk, Stark knocks him out with a loud thud.
With Ultron’s body destroyed, Wanda and Pietro take off.
HAWKEYE’S NEST
Public opinion and governments denounce the destructive actions of Hulk and Iron Man. So the Avengers decide to hide for a while.
Hawkeye proposes an unexpected place, a typical American house in the countryside. To the surprise of his colleagues, that's where he lives with his wife and two children. And his wife is expecting a baby. For security reasons, only Romanoff and Nick Fury knew about his family.
Because of his visions, Thor travels to London to seek help from Erik Selvig. He leads Thor to a special pool where, after diving, sees vital information to defeat Ultron.
Meanwhile, Tony Stark meets Nick Fury in the stable of Burton. The veteran and former director of SHIELD provides his moral support and expertise to the group to stop Ultron.
KOREA
Ultron wants to evolve by replacing its metal body with a more advanced synthetic one. So it visits Dr. Cho’s labs in Korea. Falling under the control of the scepter of Loki, Cho builds an android inside a receptacle called the ark. The android receives the scepter’s gem in its forehead, and Cho transfers Ultron’s brain into the android. But when Wanda touches the android, she discovers Ultron’s true motives, to destroy the human race. So she frees Cho, who cancels the transfer and Wanda escapes with Pietro despite Ultron’s complaints.
Fortunately, Captain America, Black Widow and Hawkeye arrive on the scene with a Quinjet thanks to Banner, who expected Ultron’s intentions. In an uneven but courageous battle, Cap faces Ultron but the balance tips in his favor when the twins join him against the villain. Meanwhile, the Black Widow delivers the ark with the android to Hawkeye, who flies off in the Quinjet. Unfortunately, Romanoff falls prisoner to Ultron.
THE VISION
At Stark labs, Tony tells Banner that he discovered JARVIS was the benevolent hacker during his visit to the Internet servers in Oslo. Stark wants to install JARVIS on the android but Banner has doubts since something similar triggered the problem with Ultron. Stark thinks JARVIS is safe and of good intentions. Banner understands and backs him. JARVIS installs on the android, merging with the previous transfer from Ultron.
But Captain America and Pietro disagree. Wanda showing up causes a lot of tension in Banner. Looks like a fight between heroes is inevitable. But Thor arrives and invoking thunder with his hammer, charges the android, who turns on and breaks out from the ark.
Thor enlightened visions led him to the conclusion that the android would be an exceptional ally to stop Ultron. The android says it is neither Ultron nor JARVIS, but intends to defend life.
Meanwhile, Romanoff reveals her location (the base in Sokovia) using Morse code. Hawkeye receives the message and notifies the group. It is time to attack the villain! Jaw dropping everyone, the android grabs Mjolnir and hands it to Thor, proving it’s worthy of joining the Avengers.
FINAL BATTLE
Ultron has built its own army of robots. As it cannot gain access to atomic missiles, Ultron wants the extinction of life the old fashion way: by using a giant meteorite. And since it cannot summon one from space, Ultron is to create one of its own. The plan is to use Chitauri technology to raise Sokovia from the ground, and drop it after reaching a considerable high altitude. It would be equivalent to the impact of a large meteorite and allow Ultron to achieve its mission. After implementing the plan, Sokovia goes up in the air.
The Avengers arrive, discover Ultron’s plan and start destroying robots. When Ultron sees the android, it refers to the android as its "vision". The Vision enters Ultron’s main program and disconnects it from the network. Thor fights Ultron and finally, Vision hits it hard using Mjolnir.
Nick Fury and Maria Hill appear in a Helicarrier and send boat ships to rescue the civilians. When only a few remain on the floating Sokovia, Ultron, piloting the Avengers’ Quinjet, fires a long burst of bullets on the heroes. Hawkeye was saving a boy but was on the exact path of fire. Pietro arrives in time to save him yet he cannot avoid the bullets himself and dies from the wounds.
Wanda goes into shock when she learns about her brother’s passing, and a robot reaches the device to cause Sokovia to collapse.
Hulk leaves the Black Widow on the Helicarrier and leaps into the Quinjet, throwing Ultron overboard. Other Avengers get to safety boarding the giant ship. Guided by Banner, Hulk puts the Quinjet in stealth mode and flies away. He wishes to seclude to avoid harming anyone.
Following Stark's instructions, Thor uses the power of Mjolnir to overload the Chitauri system. The explosion destroys Sokovia into a million pieces, nulling the threat. Iron Man barely escapes alive from this outbreak.
The few robots that remained fly off. They must destroy all since Ultron can inhabit any of them. War Machine takes care of that. But one lucky robot escapes. Not so, since the Vision finds it. After exchanging an android-to-android talk, Vision destroys Ultron.
NEW MEMBERS
A few months later, the Avengers are in their new headquarters in upstate New York. The son of Hawkeye is born without complications. Thor explains to his companions that there are six infinity gems. The Vision carries one on its forehead. Thor believes it is safe there. But someone is moving circumstances like chess pieces to get them all.
Thor returns to Asgard. The others do as well to their respective places, except for Captain America and Black Widow who stay to train the new Avengers: Falcon, War Machine, Vision and Wanda.
EPILOGUE
Smiling, Thanos wears the Gauntlet where infinity gems are to be placed.