Movie plot

Five months after Thaddeus Ross is elected President of the United States, he sends Sam Wilson and Joaquin Torres—the new Captain America and Falcon, respectively—to Oaxaca, Mexico, to stop the illegal sale of classified items stolen by the Serpent Society, a rogue special-ops team led by Sidewinder. They recover the items, but Sidewinder escapes. Torres is excited to be taking on Wilson's former mantle, but Wilson is hesitant to involve Torres in dangerous missions due to the pair not having superpowers like former Captain America Steve Rogers. After the mission, Wilson and Torres train with Isaiah Bradley, a super soldier who was imprisoned and experimented on by the U.S. government.

Ross invites Wilson and Torres to the "Celestial Island World Summit" with world leaders at the White House, and Wilson accepts on the condition that Bradley is also invited. Ross asks Wilson to help him reform the Avengers. During the summit, Ross explains that a new metal, adamantium, has been discovered on "Celestial Island", which was formed when the Celestial Tiamut emerged in the Indian Ocean.[a] The recovered items were the first refined samples of the metal and were stolen from a Japanese mining operation. To avoid an arms race, Ross proposes a treaty to govern adamantium's mining and distribution. As he is talking, the song "Mr. Blue" plays and causes several men, including Bradley, to begin shooting at Ross and other dignitaries. Apprehended by Ross's head of security, former Black Widow Ruth Bat-Seraph, the men regain their senses and deny any knowledge of the attack.

While investigating, Wilson is ambushed by Sidewinder and captures him. Torres tracks a call on Sidewinder's phone to a hidden black site in West Virginia called Camp Echo One. Ross tries to salvage the treaty, but the Japanese government blames him for the theft of their adamantium and the subsequent White House attack. Ross realizes that the mastermind of these events is Dr. Samuel Sterns, who gained advanced intelligence after being exposed to Bruce Banner's blood during the Abomination's rampage through Harlem.[b] Ross imprisoned Sterns at Camp Echo One, publicly blamed him for the Abomination's actions, and promised to release him if Sterns helped advance him to the presidency. Wilson and Torres find Sterns and learn how he uses technology and the song "Mr. Blue" to control minds. He escapes while they are fighting mind-controlled soldiers.

Bat-Seraph joins Wilson and Torres, and they meet with Wilson's military friend Dennis Dunphy, who has Sidewinder in custody. Wilson learns enough to deduce Sterns's plan to destroy Ross's reputation. Wilson, Torres, and Bat-Seraph go to Celestial Island where Ross and the Prime Minister of Japan are racing to claim ownership of adamantium. Sterns controls the minds of two American pilots who attack the Japanese fleet. Wilson and Torres intercept the planes and convince the Japanese to stand down. Torres is critically injured in the fight. Ross tells Wilson that he is dying of heart failure and had Sterns develop pills that have prolonged his life; Ross refused to release Sterns for fear that he would no longer make the pills, leading to Sterns's anger and plans for revenge.

Sterns kills Dunphy, preventing him from warning Wilson that the pills have been adding gamma radiation to Ross's body. After Wilson is consoled by his friend Bucky Barnes, Sterns surrenders himself to Wilson. Ross loses control of his emotions during a press conference and transforms into Red Hulk, destroying part of the White House. Wilson rushes to stop the rampage. Unable to overpower Ross, Wilson attempts to calm him down by reminding him of visits to Washington, D.C.'s cherry blossom trees with his estranged daughter Betty. The two fight until they are exhausted, and Ross reverts to normal. Bradley is exonerated, Wilson invites a recovering Torres to join the Avengers, the adamantium treaty is ratified, and Ross has himself incarcerated at the Raft. Wilson and Betty visit him. In a post-credits scene, an imprisoned Sterns warns Wilson of a coming attack from other worlds.