Full story
Two years after the Battle of New York, Steve Rogers lives in Washington and works for S.H.I.E.L.D. He is still adjusting to the 21st century and keeps a list of things he missed. Running laps around the Mall, he befriends Sam Wilson, an ex-soldier who now counsels veterans. On a mission to rescue hostages from a ship, Steve finds out Natasha Romanoff had secret orders from Nick Fury: copy data off the ship's computer.
Fury shows Steve Project Insight: three Helicarriers linked to satellites, built to take out threats before they happen. Steve hates it. Fury has doubts too, because he can't open the data Natasha brought back. He is ambushed in the street by assassins led by the Winter Soldier, a killer with a metal arm. Wounded, he gets to Steve's apartment, warns him that S.H.I.E.L.D. is compromised, hands him a flash drive and gets shot. He dies in the hospital, or seems to.
Alexander Pierce, Fury's boss, calls Steve in for a talk. Steve tells him nothing. In the elevator he is boxed in by agents of the S.T.R.I.K.E. team, fights them all off and becomes a fugitive. With Natasha, he follows the flash drive to an old bunker in New Jersey. There, a computer holds the mind of Arnim Zola. He explains that Hydra never died: it grew inside S.H.I.E.L.D. from the end of the war, stirring up chaos so people would trade freedom for safety. A missile levels the bunker and they barely get out.
Holed up at Sam's place, they grab Agent Jasper Sitwell and learn the plan: an algorithm built by Zola has flagged millions of people as threats, and Insight will kill them all at once. Sam joins up with his mechanical wings as the Falcon. In a highway battle, the Winter Soldier's mask comes off. It's Bucky Barnes, alive, used by Hydra as a weapon and wiped again and again. Fury turns up alive; his death was staged.
Steve tells every S.H.I.E.L.D. agent the truth over the headquarters loudspeakers. While he and Sam swap the Helicarriers' chips, a disguised Natasha disarms Pierce and dumps all of S.H.I.E.L.D.'s and Hydra's secrets online. Fury kills Pierce. On the last Helicarrier, Steve refuses to fight Bucky and tells him he is with him till the end of the line. The ships destroy each other and Steve falls into the Potomac. Bucky pulls him out and disappears. S.H.I.E.L.D. is finished. Steve and Sam set out to find Bucky. In the credits scenes, Baron Strucker keeps Loki's scepter and a pair of super-powered twins, and Bucky visits the Captain America exhibit at the museum.