Two years after the Battle of New York, Steve Rogers, also known as Captain America, is trying to adapt to modern life while working for the espionage agency S.H.I.E.L.D. in Washington, D.C. During a high-stakes mission with Agent Natasha Romanoff and her counter-terrorism team led by Agent Brock Rumlow, they confront pirates led by the elusive Georges Batroc. However, Rogers uncovers that Romanoff has a secret task: to extract crucial data from the ship's computers.
Upon returning to S.H.I.E.L.D. headquarters, known as the Triskelion, Rogers meets with Director Nick Fury, who briefs him about a dangerous initiative called Project Insight — this involves three Helicarriers linked to satellites designed to eliminate perceived threats before they arise. When Fury is unable to decrypt the sensitive data Romanoff secured, he begins to question the integrity of the Insight project and persuades Alexander Pierce, a senior official, to postpone its implementation. But danger is lurking; during a planned meeting with Maria Hill, Fury is brutally attacked by the formidable Winter Soldier, leading to a desperate escape to Rogers' apartment. In a last attempt to protect their secrets, Fury reveals to Rogers that S.H.I.E.L.D. has been infiltrated, but is fatally shot by the Winter Soldier, leaving behind a flash drive containing essential data.
When Pierce learns of Rogers withholding critical information, he declares him a fugitive. On the run, Rogers finds Romanoff, and together they uncover a hidden S.H.I.E.L.D. bunker in New Jersey containing a supercomputer that holds the consciousness of Arnim Zola. Zola divulges a chilling truth: after Rogers had defeated him in World War II, he secretly restored Hydra within the framework of S.H.I.E.L.D., orchestrating global chaos through the Winter Soldier, now revealed to be Bucky Barnes, Rogers' former best friend thought dead.
Rogers and Romanoff narrowly escape when a missile obliterates the bunker. Realizing they need help, they enlist Sam Wilson, a former USAF pararescueman who shares a friendship with Rogers, and use a high-tech Falcon wingpack he had developed in service. They also capture informant Jasper Sitwell, who unwittingly reveals that Zola's algorithm targets individuals deemed future threats to Hydra, thus justifying the operations of the Insight Helicarriers.
As events unfold, Sitwell tragically becomes a casualty during a confrontation with the Winter Soldier. In a surprising twist, Rogers discovers that Bucky has been altered and is under Hydra's control. Meanwhile, Hill rescues Rogers and Romanoff and reunites them with the apparently dead Fury, who is actually alive and plotting the downfall of Hydra by sabotaging the Helicarriers.
The day of the Helicarriers’ launch arrives. Rogers boldly exposes Hydra’s insidious plot to the world, while Romanoff adeptly disarms Pierce in disguise. Fury confronts Pierce, leading to a fatal showdown. While Rogers and Wilson manage to replace the controller chips on the Helicarriers, they are met with an intense battle against Barnes. Rogers, determined not to fight his old friend, is ultimately plunged into the Potomac River by the chaos unfolding around them. To Rogers' surprise, Barnes saves him just before disappearing into the shadows.
In the aftermath of the battle, Romanoff defends both herself and Rogers during a Senate inquiry, while Fury, cloaked under the guise of his supposed death, sets off to dismantle Hydra's remaining operations in Europe. Determined to find Bucky, Rogers teams up with Wilson, as the world grapples with the fallout from the Triskelion's destruction.
In a gripping mid-credits scene, Baron Wolfgang von Strucker is shown examining a powerful energy scepter, hinting at impending threats, while in a poignant post-credits moment, Barnes pays homage to his own memorial at the Smithsonian Institution.
