In 1991, Bucky Barnes (Sebastian Stan) is brainwashed to be the Winter Soldier.
Karpov: [in Russian, reading from a book] Longing. Rusted. Seventeen. Daybreak. Furnace. Nine. Benign. Homecoming. One. Freight Car. . . . . Good morning, Soldier.
Bucky causes a car to crash and recovers bags of a serum that turns people into super soldiers.
After the Avengers defeated Ultron, Thor and Hulk are nowhere to be found. Hawkeye (Jeremy Renner) has gone home to spend time with his family. Even Iron Man (Robert Downey Jr.) has apparently disengaged.
Captain America (Chris Evans) and Black Widow (Scarlett Johansson) are leading a new team of Avengers, consisting of Scarlet Witch (Elizabeth Olsen), Vision (Paul Bettany), War Machine (Don Cheadle) and Falcon (Anthony Mackie). But the world hasn't forgotten the numerous civilian casualties that resulted from the Avengers' previous missions.
In Lagos, Nigeria, the team is tracking the movements of Brock Rumlow (Frank Grillo), a Hydra agent who had infiltrated S.H.I.E.L.D. until Captain America exposed him. Brock was on one of the three ships that Cap had caused to fire on each other, and he managed to survive the resulting crash, but he was badly burned, and now he wears a skull mask and goes by the name Crossbones. In Lagos, Crossbones and his team of mercenaries ram a garbage truck into the Institute for Infectious Disease building and clear out the guards with smoke canisters.
Crossbones uses hydraulic gauntlets to give him super strength, and pounds open the glass around the lab. He grabs a vial containing a deadly, highly contagious virus. Cap's team takes out some of the mercenaries, and Crossbones and the rest of the men make their escape in a truck. After a chase, the truck is taken out of action. Crossbones hands the vial to one of his men, and tells them all to scatter. He then engages Cap, repeatedly punching him with enhanced strength, while the rest of the team chases after the mercenaries.
Crossbones: [to Captain America] There you are, you son of a bitch. I've been waiting for this.
Falcon finds the one holding the vial and has his droid shoot him, with Black Widow grabbing the vial before it hits the ground.
Black Widow: Thank you, Sam.
Falcon: Don't thank me.
Black Widow: I'm not thanking that thing. [referring to Sam's droid]
Falcon: His name is Redwing. He's cute. Go ahead, pet him.
The battle between Crossbones and Captain America continues.
Crossbones: This is for dropping a building on my face.
Stever rips off one of Crossbones' gauntlets and knocks him to the ground. He takes off his mask in defeat, allowing Steve to see his face for the first time.
Crossbones: I think I look pretty good, all things considered. . . You know he knew you. Your pal, your buddy, your Bucky.
Captain America: What did you say?
Rumlow: He remembered you. I was there. He got all weepy about it. Till they put his brain back in a blender. He wanted you to know something. He said to me, "Please tell Rogers. When you gotta go, you gotta go." And you're coming with me.
With Cap momentarily distracted, Crossbones pushes a button, triggering a bomb on his vest. Cap braces himself, but Scarlet Witch is able to contain the force of the explosion. She uses her powers to push it up into the air, but she's only able to elevate it a bit before she loses control, and the explosion rips into the seventh floor of a nearby hotel. Cap calls for fire and rescue, and then runs into the building to help evacuate. Wanda tearfully looks at the destruction.
In a theater inside Tony Stark's old college, a video plays of him and his parents, Howard (John Slattery) and Maria.
Maria Stark: Be nice, dear. He's been studying abroad.
Howard Stark: Really, which broad? . . . You know, they say sarcasm is a metric for potential. If that's true, you'll be a great man some day.
At the end, Tony tells the students that he is starting the Howard and Maria Stark Foundation, and each one of them has been approved for a research grant. In a corridor, a woman confronts him.
Miriam: They say there is a correlation between generosity and guilt.
Miriam shows him a picture of her son, who had been killed in Sokovia, crushed by a building that the Avengers had knocked down.
At the Avengers' headquarters, the team is watching news footage of the Lagos mission. The reporter says that eleven people were killed in the hotel.
King T'Chaka: [on TV] Our people's blood is spilled on foreign soil. Not only because of the actions of criminals, but by the indifference of those pledged to stop them. Victory at the expense of the innocent is no victory at all.
Steve is trying to consul Wanda who is blaming herself.
Rogers: I should've clocked that bomb vest long before you had to deal with it. Rumlow said 'Bucky' and all of a sudden I was a 16-year-old kid again, in Brooklyn. And people died. It's on me. . . This job. We try to save as many people as we can. Sometimes that doesn't mean everybody. But if we can't find a way to live with that, next time . . . maybe nobody gets saved.
Vision tells Steve that Tony has arrived, and he brought the Secretary of State as a guest. General Thaddeus Ross (William Hurt) had been involved in the experiment that turned Bruce Banner into the Hulk, and then had spent years trying to hunt him down.
Ross: Five years ago, I had a heart attack. I dropped right in the middle of my backswing. Turned out it was the best round of my life because after thirteen hours of surgery and a triple bypass, I have found something forty years in the army had never taught me . . . perspective. The world owes the Avengers an unpayable debt. You have fought for us, protected us, risked your lives. But while a great many people see you as heroes, there are some who would prefer the word "vigilantes".
Natasha: And what word would you use, Mr. Secretary?
Ross: How about "dangerous"? What would you call a group of US based, enhanced individuals who routinely ignore sovereign borders and inflict their will wherever they choose and who, frankly, seem unconcerned with what they leave behind? New York, Washington D.C., Sokovia, Lagos.
Ross shows pictures of the destruction that follows the team wherever they go.
Rogers: Okay. That's enough.
Ross: In the past four years, you've operated with unlimited power and no supervision. That's an arrangement the governments of the world can no longer tolerate.
Ross sets a thick document down on the table and tells them it's the Sokovia Accords, ratified by 117 countries. The accords state that the Avengers will operate under a panel's supervision, only acting when the panel decides it's necessary.
Ross: Tell me, Captain, do you know where Thor and Banner are right now? 'Cause you can bet if I misplaced a couple of 30 megaton warheads, there'd be consequences.
Ross says there will be a meeting in Vienna in three days, and if they don't sign on, they'll have to retire. Meanwhile, in Cleveland, a young man later revealed as Zemo (Daniel Brühl), tricks a Russian into letting him into his home. He recovers Russian files and a red book with a black star on the cover.
Zemo: Mission Report: December 16, 1991. When S.H.I.E.L.D. fell, Black Widow released Hydra files to the public. Millions of pages. Much of it encrypted, not easy to decipher, but I have experience and patience. A man can do anything if he has those.
The Russian is a colonel in hiding, which Zemo has the colonel's head partly submerged in a sink of water. When the colonel refuses to divulge details about the 1991 mission, Zemo drowns him.
Back at the Avengers' headquarters, the team spends hours debating whether to agree to the accords.
Rhodes: Secretary Ross has a Congressional Medal of Honor, which is one more than you have.
Sam: So let's say we agreed to this thing. How long is it gonna be before they lojack us like a bunch of common criminals?
Rhodes: 117 countries wanna sign this. 117, Sam, and you're just like, "Nah, it's cool."
Sam: How long are you gonna play both sides?
Vision: I have an equation.
Sam: [sarcastically] Oh, this'll clear it up.
Vision: In the 8 years since Mr. Stark announced himself as Iron Man, the number of known enhanced persons has grown exponentially. And during the same period, a number of potentially world-ending events has risen at a commensurable rate.
Rogers: Are you saying it's our fault?
Vision: I'm saying there may be a causality. Our very strength invites challenge. Challenge incites conflict. And conflict breeds catastrophe. Oversight is not an idea that can be dismissed out of hand.
Natasha: Tony? You are being uncharacteristically non-hyperverbal.
Rogers: That's 'cause he's already made up his mind.
Tony: Boy, you know me so well. Actually, I'm nursing an electromagnetic headache. That's what's going on, Cap. It's just pain. It's discomfort. Who's putting coffee grounds in the disposal? Am I running a Bed and Breakfast for a biker gang?
Tony puts a phone on the table, a screen pops up.
Tony: Oh, that's Charles Spencer, by the way. He's a great kid. Computer engineering degree, 3.6 GPA. Had a floor-level gig, an intel plan for the fall. But first he wanted to put a few miles on his sole before he parked it behind a desk. See the world, maybe be of service. Charlie didn't wanna go to Vegas or Fort Lauderdale, which is what I would do. He didn't go to Paris or Amsterdam, which sounds fun. He decided to spend his summer building sustainable housing for the poor.
Guess where: Sokovia. He wanted to make a difference, I suppose. I mean, we won't know because we dropped a building on him while we were kickin' ass. There's no decision-making process here. We need to be put in check! And whatever form that takes, I'm game. If we can't accept limitations, we're boundaryless, we're no better than the bad guys.
Rogers: Tony, if someone dies on your watch, you don't give up.
Tony: Who said we're giving up?
Rogers: We are if we're not taking responsibility for our actions. This document just shifts the blame.
Rhodes: Sorry, Steve, that is dangerously arrogant. This is the United Nations we're talking about. It's not the World Security Council, it's not S.H.I.E.L.D., it's not Hydra.
Rogers: No, but it's run by people with agendas and agendas change.
Tony: That's good! That's why I'm here. When I realized what my weapons were capable of in the wrong hands, I shut it down. Stopped manufacturing.
Rogers: Tony, you chose to do that. If we sign this, we surrender our right to choose. What if this panel sends us somewhere we don't think we should go? What if there's somewhere we need to go and they don't let us? We may not be perfect but the safest hands are still our own.
Tony: If we don't do this now, it's gonna be done to us later. That's the fact. That won't be pretty.
Wanda: You're saying they'll come for me.
Vision: We would protect you.
Natasha: Maybe Tony's right. If we have one hand on the wheel, we can still steer. If we take it off . . .
Sam: Aren't you the same woman who told the government to kiss her ass a few years ago?
Getting nowhere, Steve leaves in disgust after receiving a message on his phone. He attends the funeral of Peggy Carter. Her niece Sharon Carter (Emily VanCamp), speaks at the funeral.
Sharon Carter: Margaret Carter was known to most as the founder of S.H.I.E.L.D. . . but I just knew her as Aunt Peggy. She had a photograph in her office. Aunt Peggy standing next to JFK. As a kid that was pretty cool. But it was a lot to live up to, which is why I never told anyone we were related. I asked her once how she managed to master diplomacy and espionage at a time when no one wanted to see a woman succeed at either. And she said, "Compromise where you can, but where you can't, don't. Even if everyone is telling you that something wrong is something right. Even if the whole world is telling you to move, it is your duty to plant yourself like a tree, look them in the eye, and say, 'No, you move'."
Later, Natasha finds him in the old church alone. She tells him that she, Tony, James Rhodes and Vision had signed on, with Clint and Wanda holding out.
Rogers: Who else signed?
Natasha: Tony, Rhodey, Vision.
Natasha: Says he's retired.
Natasha: TBD. I'm off to Vienna for the signing of the Accords. There's plenty of room on the jet. Just because it's the path of least resistance doesn't mean it's the wrong path. Staying together is more important that how we stay together.
Rogers: What are we giving up to do it? . .. I'm sorry, Nat. I can't sign it.
Natasha: I know.
Rogers: Then what are you doing here?
Natasha: I didn't want you to be alone.
In Vienna, several heads of state have gathered for the ratification of the accords. Natasha meets the prince of Wakanda, T'Challa (Chadwick Boseman), and his father, King T'Chaka (John Kani). T'Challa supports the accords, but not the politics behind it.
T'Challa: Two people in a room can get more done than a hundred.
King T'Chaka: Unless you need to move a piano.
King T'Chaka takes the podium for the keynote address.
King T'Chaka: When stolen Wakandan vibranium was used to make a terrible weapon, we in Wakanda were forced to question our legacy. Those men and women killed in Nigeria were part of a goodwill mission from a country too long in the shadows. We will not however, let misfortune drive us back. We will fight to improve the world we wish to join.
T'Challa notices security personnel surrounding a van parked outside. He tries to warn others to take cover, but an explosion rips through the building, killing the king.
Back in the U.S., Steve is with Sharon Carter at the hotel, when Sam shows him a news report on the destruction in Vienna. The TV broadcast includes Security footage showing the man who planted the bomb, and Steve realizes that it's Bucky. Finishing up a phone call, Sharon tells Steve that she has to go to work. Sometime later, we see her at the explosion site. Natasha sees T'Challa nearby sitting on a bench in a stunned state and offers an apology.
T'Challa: In my culture, death is not the end. It's more of a stepping-off point. You reach out with both hands and Bast and Sekhmet, they lead you into the green veldt where you can run forever.
Natasha: That sounds very peaceful.
T'Challa: My father thought so. I am not my father.
Natasha: T'Challa, Task Force will decide who brings in Barnes.
T'Challa: Don't bother, Ms. Romanoff. I'll kill him myself.