The film opens in the present day with the discovery of an advanced aircraft frozen in the Arctic. A team of American agents investigates and finds a round red, white, and blue shield under the ice….
The story shifts back to 1942: Nazi troops led by Johann Schmidt, head of the German arcane sciences division Hydra, invade a church in Norway, where they recover an object that was once in Odin’s treasure chamber—a glowing blue cube….
In New York, small and skinny Steve Rogers tries to enlist in the military but is rejected because of his health. Later at the movies he tells a patron heckling a war-related newsreel to shut up and the fellow beats him up in the alley afterwards. But Steve refuses to stop fighting and has to be rescued by his pal James "Bucky" Barnes. Steve is jealous and disheartened to hear that Bucky has been assigned to the 107th Infantry, Steve’s fathers’ old regiment. Bucky tries to console hi pal by inviting him on a double date to the Stark exposition, where the famed inventor Howard Stark is demonstrating his new flying car—which doesn’t work. [This is the same expo mentioned as history in IRON MAN 2.] Steve excuses himself to stop by a recruiting station to try once again to sign up. His impassioned speech to Bucky about his need to stop Hitler is overheard by Professor Erskine. In the exam room, Erskine recruits Steve for a secret project and he is whisked off to Camp Lehigh to begin basic training. There he comes under the command of Col. Chester Phillips who clearly considers him unfit for the assignment; Steve also encounters brash bully Gilmore Hodge and British agent Peggy Carter. At the camp, he is harassed by his compatriots but he also distinguishes himself by first, being the first soldier to retrieve the flag from the top of the flagpole. He does this not by trying to climb the pole like everyone else but by removing the metal pin that holds the pole upright. Secondly, Phillips tosses a (dummy) grenade into the midst of the soldiers and Steve throws himself on it to protect the others rather than ducking for cover.
The night before the experiment, Erskine meets with Steve to explain why he was chosen; the scientist relates how he was forced to create the serum back in Germany where he tested it on his assistant Johann Schmidt. Schmidt ended up with superpowers, and some unfortunate side effects (to be revealed later). Steve was chosen because as a weak man, he understands the value of strength, and the serum enhances a man’s qualities so a good man will become better—unlike Schmidt…..
Meanwhile Schmidt has had his chief scientist Arnim Zola experimenting with the Cosmic Cube as a power source for fantastic weapons. He murders three emissaries from Hitler with a Cube-powered ray gun, since Hydra has moved beyond the goals of the Nazis. Learning that Erksine has been located, he gives the order to have him eliminated….
The next day, Steve is taken by Peggy to a secret lab where he is injected with the Super-Soldier Serum and bombarded with Vita-Rays, controlled by Howard Stark. He emerges from the capsule a larger more muscular man. A Hydra spy planted among the dignitaries sets off a bomb and shoots Prof. Erskine then flees into the street. Steve pursues and after a wild chase and gun battle apprehends the killer as he tries to escape in a minisub. Back at the lab, they discover that Erskine’s formula cannot be duplicated, dashing Phillips’ hopes of creating a Super-Soldier Army; the Colonel wants nothing more to do with Steve Rogers. At this point a Senator steps forward to recruit Steve for a mission…
…which turns out to be touring the country wearing a red-white-and-blue costume in a patriotic show to sell war bonds. Captain America becomes a sensation, starring in shows, movies, even his own comic book! But he feels he is not really making a contribution. During an appearance before American troops in Europe, Cap is heckled by soldiers who have seen real combat, and have no respect for an entertainer in a silly costume. He finds Peggy Cater on the scene, along with Col. Phillips. Learning that the audience consists of survivors of a disastrous mission by the 107th Infantry, Bucky Barnes’ unit, he asks Phillips for permission to mount a rescue for any troops who may be prisoners. Phillips dismisses his suggestion with contempt. Peggy arranges for Howard Stark to fly Steve behind enemy lines. He makes his way into the Hydra base and frees hundreds of prisoners, who turn the base into chaos. Steve rescues Bucky from a lab and they come face to face with Schmidt, who taunts Steve as a "superman" who only has the imagination to follow his country’s orders. The two fight briefly and Schmidt removes his human mask to reveal a crimson skull-like face, the effect of the Serum on him. The entire complex explodes from the Red Skull’s pre-set bombs as the villain escapes…. Later, as Col. Phillips is drafting the press release that Captain America has been killed, Cap shows up with 400 rescued prisoners and captured Hydra technology….
Cap being celebrated as a hero puts a strain on Steve and Peggy’s budding romance. When he is in Starks’ lab to receive a more militarily efficient outfit, he discovers a shield-like disc of the rare metal Vibranium, which is lightweight and absorbs impacts. Peggy "tests" it by firing a gun at Steve. The shield works. Cap assembles a team of Howling Commandos from among the prisoners he rescued, including Bucky. He leads them in action against the known Hydra bases (Cap had seen a map of them during his rescue mission). Cap and the Commandos then attack the train carrying Arnim Zola through the mountains; Cap and Bucky enter the train while Gabe Jones waits on the roof. In the violent battle for the train, Bucky falls to his death from a hole blasted in the car’s side, but Zola is captured. The sinister scientist is interrogated by Col. Phillips and bows to the American’s threats. From Zola’s information they know the last Hydra base is in the Alps. Cap leads the Howling Commandos in a frontal assault. The fighting is furious as the sinister organization’s agents refuse to surrender. The chief villain and his cadre of supporters manage to escape to his advanced aircraft to carry out their deadly mission against New York. As the Red Skull’s plane takes off, Cap runs to catch it but falls behind—until Phillips and Peggy pick him up in Schmidt’s limousine. As the plane finally leaves the runway, Cap leaps and catches hold of the landing gear. Entering the craft, he battles the villain’s minions then comes face to face with his nemesis. After a furious fight with the Red Skull, Cap’s shield damages the machine housing the Cosmic Cube. The Skull extracts it and the godlike device glows brighter until the Skull vanishes—either disintegrated or absorbed. The Cube then burns a hole through the floor and drops into the ocean. Cap tries to turn the craft from its deadly mission in New York but realizes that his only option is to crash the plane into the arctic wastes. He speaks to Peggy over the radio, filling her in on his actions and she tries to cover her knowledge that Steve will not survive by making a date with him for Saturday night---then Steve’s voice is cut off….
In the days that follow, Howard Stark in an advanced submarine manages to trace and recover the Cosmic Cube, but he finds no sign of Captain America. The Army—and Peggy Carter—go on without him, but his heroic sacrifice inspires the nation.
Suddenly, Steve awakens in a hospital room in what appears to be the 1940s but he is suspicious: the baseball game playing on the radio is from 1941. He breaks out of the room, which is revealed to be a stage set and races through the building out into a Times Square that looks utterly unfamiliar to him. He is met by Colonel Nick Fury who apologizes for the charade, they merely wanted to make the bad news easier for him to digest…he has been asleep for nearly seventy years. Steve reacts, "I had a date."
EPILOGUE: After the credits Steve is training on a heavy bag when Nick Fury mentions he has a mission for him, "You’re not the only hero." Then we get a teaser trailer for THE AVENGERS.