Two years after the Battle of New York, Steve Rogers works in Washington, D.C., for the espionage agency S.H.I.E.L.D. under Director Nick Fury, while adjusting to contemporary society. Rogers and Agent Natasha Romanoff are sent with S.H.I.E.L.D.’s counter-terrorism S.T.R.I.K.E. team, led by Agent Rumlow, to free hostages aboard a S.H.I.E.L.D. vessel from pirates led by Georges Batroc. Mid-mission, Rogers discovers Romanoff has another agenda: to extract data from the ship’s computers for Fury. Rogers returns to the Triskelion, S.H.I.E.L.D.’s headquarters, to confront Fury and is briefed about Project Insight: three Helicarriers linked to spy satellites, designed to preemptively eliminate threats. Unable to decrypt the data recovered by Romanoff, Fury becomes suspicious about Insight and asks senior S.H.I.E.L.D. official and Secretary of Internal Security Alexander Pierce to delay the project.
On his way to rendezvous with Maria Hill, Fury is ambushed by assailants led by a mysterious assassin called the Winter Soldier. Fury escapes to Rogers’ apartment, and warns Rogers that S.H.I.E.L.D. is compromised. Fury is gunned down by the Winter Soldier, before handing Rogers a flash drive containing data from the ship. Fury is pronounced dead during surgery, and Hill recovers the body. The next day, Pierce summons Rogers to the Triskelion. When Rogers withholds Fury’s information, Pierce brands him a fugitive. Hunted by S.T.R.I.K.E., Rogers meets with Romanoff. Using data in the flash drive, they discover a secret S.H.I.E.L.D. bunker in New Jersey, where they activate a supercomputer containing the preserved consciousness of Arnim Zola. Zola reveals that ever since S.H.I.E.L.D. was founded after World War II, Hydra has infiltrated and secretly operated within its ranks, sowing global chaos with the objective of making humanity surrender its freedom in exchange for security. The pair narrowly escape death when a S.H.I.E.L.D. missile destroys the bunker, and realize that Pierce is Hydra’s leader within S.H.I.E.L.D.
Rogers and Romanoff enlist the help of former USAF pararescueman Sam Wilson, whom Rogers befriended, and acquire his powered “Falcon” wingpack. Deducing that S.H.I.E.L.D. agent Jasper Sitwell is a Hydra mole, they force him to divulge that Zola developed a data-mining algorithm that can identify individuals becoming threats to Hydra. The Insight Helicarriers will sweep the globe, using satellite-guided guns to eliminate these individuals. Rogers, Romanoff, and Wilson are ambushed by the Winter Soldier, who kills Sitwell. During the fight, Rogers recognizes the Winter Soldier as Bucky Barnes, his childhood best friend who supposedly fell to his death on a mission, but was actually captured and experimented upon after WWII. Hill manages to extract the trio to a safehouse where Fury, who had faked his death, is waiting with plans to sabotage the Helicarriers by replacing their controller chips.
After the World Security Council members arrive for the Helicarriers’ launch, Rogers broadcasts Hydra’s plot to everyone at the Triskelion. Romanoff, disguised as one of the Council members, disarms Pierce. Fury arrives and forces Pierce to unlock S.H.I.E.L.D.’s database so that Romanoff can leak classified information, exposing Hydra to the public. Following a struggle, Fury kills Pierce. Meanwhile, Rogers and Wilson storm two Helicarriers and replace the controller chips, but the Winter Soldier destroys Wilson’s suit and fights Rogers on the third. Rogers fends him off and replaces the final chip, allowing Hill to take control and have the vessels destroy each other. Rogers refuses to fight the Winter Soldier in an attempt to reach his friend, but as the ship collides with the Triskelion, Rogers is thrown out into the Potomac River. The Winter Soldier rescues the unconscious Rogers before disappearing into the woods. With S.H.I.E.L.D. in disarray, Romanoff appears before a Senate subcommittee, while Fury, under the cover of his apparent death, heads to Eastern Europe in pursuit of Hydra’s remaining cells. Rogers and Wilson decide to find the Winter Soldier, while Rumlow, who was a double agent for Hydra, is hospitalized following the Triskelion’s destruction.
In a mid-credits scene, Baron Wolfgang von Strucker, at a Hydra lab, proclaims that the “age of miracles” has begun as scientists examine an energy-filled scepter and two test subjects: one with superhuman speed, the other with telekinetic powers. In a post-credits scene, Barnes visits his own memorial at the Smithsonian Institution.
In Captain America: Winter Soldier we are introduced to Bucky Barnes. Bucky was also experimented on but by the Evil Arnim Zola. Bucky becomes a brainwashed assassin during World War II. Thanks to the Avengers, they connect with Bucky, aka Winter Soldier, who turned his back on Arnim Zola to become an Avenger. This film is not as forgotten as others but also isn’t a major piece to the puzzle. While it does introduce Winter Soldier in the same timeline as Captain America. We do see more glimpses of Bucky later on in the Avengers but more as a supporting role.