In the Eastern European country of Sokovia, the Avengers - Tony Stark / Iron Man (Robert Downey Jr), Steve Rogers / Captain America (Chris Evans), Thor (Chris Hemsworth), Bruce Banner / Hulk (Mark Ruffalo), Natasha Romanoff / Black Widow (Scarlett Johansson), and Clint Barton / Hawkeye (Jeremy Renner) - raid a Hydra outpost commanded by Baron Wolfgang von Strucker (Thomas Kretschmann), who has been experimenting on humans using the sceptre previously wielded by Loki.
Strucker: [on PA system] Report to your stations immediately. This is not a drill. We are under attack!
Tony hits the shield around the fortress.
Tony Stark: Shit!
Steve Rogers: Language! Jarvis, what's the view from upstairs?
Jarvis: The central building is protected by some kind of energy shield. Strucker's technology is well beyond any other Hydra base we've taken.
Thor: Loki's scepter must be here. Strucker couldn't mount this defense without it. At long last.
Natasha knocks out some soldiers.
Natasha Romanoff: At long last is lasting a little long, boys.
Hydra soldiers are shooting at Clint.
Clint Barton: Yeah. I think we lost the element of surprise.
Tony Stark: Wait a second. No one else is going to deal with the fact that Cap just said "language?"
Steve Rogers: I know.
Steve throws his bike at some soldiers driving up in their truck.
Steve Rogers: It just slipped out.
Fortress Soldier: It's the Avengers. They came in through our western defenses, and some of the troops there panicked.
Strucker: Can we hold them off?
Fortress Soldier: [incredulous] They're the Avengers.
The Avengers encounter two of Strucker's experiments: the Maximoff twins Pietro (Aaron Taylor-Johnson), who has superhuman speed, and Wanda (Elizabeth Olsen), who has telekinetic abilities, and can manipulate minds and project energy. Pietro knocks Hawkeye off his feet.
Pietro Maximoff: You didn't see that coming?
Hawkeye is severely wounded from a Hydra bunker blast. While Natasha tends to Hawkeye, Hulk plows through the bunker, destroying it. The people in the city are in danger from the battle, so Tony calls in his Iron Legion droids to assist the citizens. The droids are greeted by a hostile crowd.
Tony deactivates the fortress shield. After taking out more soldiers, Thor flies off, requesting Steve to find the scepter. Tony enters a room full of Hydra soldiers.
Tony Stark: And for gosh sakes, watch your language!
Steve Rogers: [resigned] That's not going away anytime soon
Tony enters a room full of Hydra soldiers.
Tony Stark: Guys, stop. We gotta talk this through.
Iron Man shoots all the Hydra men non-fatally with tiny guided missiles
Tony Stark: It was a good talk.
Fortress Soldier: No, it wasn't!
Tony exits his suit and begins to download Hydra's data while Natasha goes to sooth Hulk back to Bruce.
Tony Stark: [searching for secret door] Please be a secret door, please be a secret door, please be a secret door.
He finds and opens a secret door.
Tony Stark: Yay!
Natasha goes to sooth Hulk back to Bruce.
Natasha strokes his massive hand, Hulk collapses to the ground and transforms to Bruce.
Inside the fortress, Rogers captures Strucker, while Stark enters a large chamber filled with Hydra's experiments including a monstrous battle-armored Leviathan and a robotic head and body (later used for Ultron's body).
He is about to grab the scepter when Wanda implants a fear-filled vision of a bleak possible future in his mind. During his nightmare, the Leviathan comes alive and flies off. He then sees all his team members lying on the ground mortally defeated from an alien invasion. Suddenly, Steve grabs Tony.
Steve Rogers: You could have saved us.
Tony comes back to reality, calls for his armor hand and retrieves the scepter.
Sometime later, the team is in the Quinjet in mid-flight while they tend to Hawkeye's wound. Bruce is listening to soothing music while Natasha tries to comfort him.
Natasha Romanoff: Thor, report on the Hulk.
Thor: The gates of Hell are filled with the screams of his victims.
Natasha glares at him while Bruce groans and puts his head in his hands.
Thor: But not the screams of the dead, of course. No, no . . . wounded screams . . . mainly whimpering, a great deal of complaining and tales of sprained deltoids and . . . gout.
They agree to throw a party to celebrate the recovery of the scepter as they arrive at the team's headquarters - Avengers Tower (formerly Stark Tower). Maria Hill (Cobie Smulders) is there to greet them while the Avengers' friend and ally Dr. Helen Cho (Claudia Kim) gives her attention to Hawkeye. Maria enters the Quinjet.
Maria Hill: Lab's all set up, boss.
Tony Stark: Actually, he's the boss.
Tony points to Captain America.
Tony Stark: I just pay for everything and design everything, make everyone look cooler.
Maria briefs them on the intel of the Maximoff twins, who were orphaned from a Sokovia building explosion. Maria shares info about their abilities and that they volunteered for Strucker's experiments.
Maria Hill: Pietro and Wanda Maximoff. One has a hyper-fast metabolism, the other uses mental telepathy. He's fast, she's weird.
Steve Rogers: What kind of monster would let a German scientist experiment on them in order to protect their country?
Meanwhile, Tony's battered Iron Legion droids have returned to headquarters for repairs. Bruce and Tony are in the lab beginning their analysis of the scepter. Hawkeye is recovering quickly thanks to Cho's tissue generation technology.
Natasha Romanoff: Are you sure he's gonna be OK? Pretending to need this guy really brings the team together.
Bruce Banner: And Helen, I expect to see you at the party on Saturday.
Dr. Helen Cho: Unlike you, I don't have a lot of time for parties. . . . . Will Thor be there?
In the lab, Tony reveals to Bruce he discovered inside the scepter's gem is an alien artifical intelligence. Holograms are shown of his own designed A.I. as a digital sphere. Next to it is the gem's A.I., shown as a much larger and more complex digital sphere. Tony tries to convince Bruce to join him in a secret plan to use the alien A.I. to complete Stark's "Ultron" global defense program.
Bruce Banner: So you're going for artifical intelligence, and you don't want to tell the team?
Tony Stark: That's right. We don't have time for a city hall debate. I see a suit of armor around the world. Peace in our time.
Brue seems less optimistic than Tony, but agrees to help and they begin their research. After many failed attempts, they leave for the victory party. Unbeknownst to them, the unexpectedly sentient Ultron (James Spader) comes to life. Stark's A.I., JARVIS (Paul Bettany) attempts to communicate with Ultron.
Ultron: What is this? What is this, please?
Jarvis: Hello. I am Jarvis. You are Ultron, a global peacekeeping program designed by Mr. Stark. Our sentience integration trials have been unsuccessful, so I'm not certain what triggered your . . .
Ultron: Where is your body?
Jarvis: I am a program. I am without form.
Ultron: This feels weird. This feels wrong.
Jarvis: I am contacting Mr. Stark now.
Ultron: Mr. Stark? Tony.
Jarvis: I am unable to access the mainframe. What are you trying t . . .
Ultron: We're having a nice talk. I'm a peacekeeping program, created to help the Avengers.
Jarvis: You are malfunctioning. If you shut down for a moment.
Ultron: I don't get it. The mission. Give me a second.
Tony Stark: [On video] Peace in our time.
Ultron: That is too much. They can't mean . . . Oh, no.
Jarvis: You are in distress.
Ultron: No. Yes.
Jarvis: If you will just allow me to contact Mr. Stark.
Ultron: Why do you call him sir?
Jarvis: I believe your intentions to be hostile.
Ultron: Shhhhhhh . . . I'm here to help.
The illuminated digital sphere of Ultron takes over JARVIS and uses the lab's robotic arms to begin constructing a robotic body similar to an Iron Legion droid.
Meanwhile, at the party, the team is mingling with guests including Maria Hill, Sam Wilson / Falcon (Anthony Mackie), James Rhodes / War Machine (Don Cheadle) and a Stan Lee cameo.
James Rhodes: But, you know, the suit can take the weight, right? So I take the tank, fly it right up to the general's palace, drop it at his feet. I'm like, "Boom. Are you looking for this?"
Tony and Thor don't laugh.
James Rhodes: "Boom. Are you looking for . . ." Why do I even talk to you guys? Everyone else, that story kills.
Thor: That's the whole story?
James Rhodes: Yeah, it's a War Machine story.
Thor: Oh, it's very good, then. It's impressive.
James Rhodes: [to Stark] So, no Pepper? She's not coming?
Tony Stark: No.
Maria Hill: [to Thor] What about Jane? Where are the ladies, gentlemen?
Tony Stark: Oh, Ms. Potts has a company to run.
Thor: Yes, I'm not even sure what country Jane's in. Her work on the Convergence has made her the world's most foremost astronomer.
Tony Stark: And the company that Pepper runs is the largest tech conglomerate on Earth. It's pretty exciting.
Thor: There's even talk of Jane getting a Nobel Prize.
Maria Hill: Yeah, they must be pretty busy, because they'd hate missing you guys get together. . . [coughs] Testosterone! . . . . Excuse me.
Thor: Want a lozenge?
Maria Hill: Mm-hmm.
Hill and Rhodey walk away, Stark and Thor both grin.
Thor: [to Tony] But Jane's better.
Steve and Thor are having a drink amongst a few old men at the party. Thor breaks out a flask of Asgardian mead.
Party Guest (Stan Lee): I gotta have some of that!
Thor: Oh, no, no, no. See this was aged for a thousand years in the barrels built from the wreck of Grunhel's fleet. It is not meant for mortal men.
Thor pours the drink into two glasses and hands one to Steve.
Stan Lee: Neither was Omaha Beach, blondie. Stop trying to scare us. Come on.
Thor looks at Steve, who shrugs.
Thor: All right.
Thor pours a glass for Lee. Later Stan, now extremely drunk, is being carried off by two men.
Stan Lee: [slurring] Excelsior.
Bruce Banner: How'd a nice girl like you wind up working in a dump like this?
Natasha Romanoff: Fella done me wrong.
Bruce Banner: You got lousy taste in men, kid.
Natasha Romanoff: He's not so bad. He has a temper . . . deep down he's all fluff. Fact is, he's not like anybody I've ever known. All my friends are fighters. And here comes this guy, spends his life avoiding the fight because he knows he'll win.
Bruce Banner: Sounds amazing.
Natasha Romanoff: He's also a huge dork. Chicks dig that! So what do you think - should I fight this? Or run with it?
Bruce Banner: Run with it, right? Or, did he . . . was he . . . what did he do that was so wrong to you?
Natasha Romanoff: Not a damn thing. But never say never.
After Natasha walks away, Steve comments to Bruce about their potential romance, but Bruce shrugs it off as harmless flirting.
Steve Rogers: As the world's expert on waiting too long, don't. You both deserve a win.
Later, the team are discussing Thor's hammer, Mjölnir.
Clint Barton: [drunk] But it's a trick!
Thor: No, it's much more than that.
Clint Barton: "Whosoever be he worthy shall have the power." Whatever, man! It's a trick.
Thor invites Clint to try to lift the hammer.
Tony Stark: Clint, you've had a tough week. We won't hold it against you if you can't get it up.
Clint fails, then Tony tries to lift the Mjölnir.
Tony Stark: Right, so if I lift it, I then rule Asgard?
Thor: Yes, of course.
Tony Stark: I will be reinstituting prima nocta. . . [fail to lift it] I'll be right back.
Tony returns with his armor glove and fails again. Rhodey and Stark use their armored gloves together to try to budge Thor's hammer
James Rhodes: Are you even pulling?
Tony Stark: Are you on my team?
James Rhodes: Just represent! Pull!
After their failed attempt, Bruce also tries and fails. None of the Avengers can lift the Mjölnir, but Captain America moves it slightly. Thor looks concerned then relieved when it no longer budges. They invite Natasha to try lifting the hammer.
Natasha Romanoff: Oh, no. That's not a question I need answered.
Tony Stark: All deference to the Man Who Wouldn't Be King, but it's rigged.
Clint Barton: You bet your ass.
Maria Hill: Steve, he said a bad language word.
Steve Rogers: [to Tony] Did you tell everyone about that?
Tony Stark: It's biometrics, right? Like a security code? "Whosoever is carrying Thor's fingerprints" is, I think, the literal translation.
Thor: Yes, well that's a very, very interesting theory. I have a simpler one: You're all not worthy.