The film opens in the present day with the discovery of a buried aircraft in the Arctic. When American agents investigate, they find a rounded red, white, and blue shield under the ice…
The story shifts back to 1942: Nazi troops led by Johann Schmidt, the head of a German sciences division called Hydra, invade a church in Norway to recover a hidden object that was once in Odin’s treasure chamber—a glowing blue cube…
In New York, Steve Rogers, a short and skinny young man, unsuccessfully tries to enlist in the military, but because of his poor overall health and physical condition, he gets rejected once again. At a movie theater, he makes a bully mad, and gets beaten in an alley. Steve refuses to quit and his pal James "Bucky" Barnes saves him.
Bucky is wearing a war uniform. They just assigned him to the 107th Infantry. Bucky tries to console hi pal by inviting him on a double date to an Exposition by famed inventor Howard Stark. Uninterested by either the inventions or his date, Steve stops by another military recruiting station and Bucky caught him. Professor Erskine, who is looking for candidates for his Super Soldier program, overhears Steve’s explanation about wanting to do something for his country in the lines.
In the exam room, Erskine meets Rogers and questions him to confirm that he is a brave, good man. Finally, the doctor signs his approval form to enlist Rogers as a soldier.
They send Rogers off to Camp Lehigh for training. The camp is under the command of Col. Chester Phillips, who clearly considers Rogers unfit for the assignment. Steve also encounters brash bully Gilmore Hodge and pretty British agent Peggy Carter, who he falls in love at first sight.
At the camp, Rogers proves being the weakest but also the smartest and bravest. On one occasion, Phillips tosses a grenade into the midst and it is Steve who throws himself on it to protect everyone. Steve is also the only one who can get a flag by using his wits. This makes Erskine select Steve as the 1st to receive the super soldier serum,
Before the experiment, Erskine revealed to Rogers that Johann Schmidt had been previously administered the serum. The serum wasn't ready. It made Schmidt stronger, but not without side effects. It also increased Schmidt's evil ways. The serum amplifies the qualities of a person. In Steve's case, he was chosen because, being weak, he understands the value of strength and will respect it. Being a good man will just make him even better.
Meanwhile, Schmidt has his chief scientist Arnim Zola experimenting with the glowing cube, the Cosmic Cube, to power new weaponry. The experiment is a success. Hydra could now use those weapons to rule the world. After murdering three emissaries sent by Hitler, Hydra separates from the Nazis.
Schmidt learns Erksine has been in NY and gives the order to eliminate him.
The next day, Peggy takes Steve to the secret Super Soldier lab. Witnessed by Colonel Phillips and other high-level staff, Rogers enters a machine, they inject him with the Super-Soldier Serum and he gets bombarded with Vita-Rays. Howard Stark controls the entire process. Rogers cries in pain but begs to receive the serum at full power. Devices short-circuit, and it first seems that Rogers did not survive the ordeal. But he emerges a foot taller and very muscular from the capsule after the unbelieving eyes of everyone, including Peggy's.
At that moment, a Hydra spy sets a bomb off to cause confusion, shoots Erskine fatally and makes his way out, shooting everyone out of his way. Erskine reminds Steve to be a good man before passing away and he pursues the villain on foot. Rogers realizes he can run fast enough to catch the car. After a wild chase, he apprehends the killer as he tries to escape in a minisub. During the fight, the last tube of serum was destroyed. And Hydra agents swallow venom to avoid becoming captive of his enemies.
Back at the lab, they discover they cannot duplicate Erskine's formula, which dashes Phillips' hopes of creating a super-soldier army. The Colonel wants nothing more to do with Steve Rogers. 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 as Captain America
Captain America becomes a sensation, starring in shows, movies, even his own comic book! But Rogers feels he is not really contributing.
During an appearance before American troops in Europe, soldiers who have seen actual combat heckle Cap. They 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 comprises 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. Rogers jumps off the plane and makes his way into the Hydra base, freeing hundreds of prisoners who turn the base into chaos. Finally, Steve finds and rescues Bucky in a lab and as they escape the facilities, being in self-destruction, come face to face with Schmidt. Cap and Schmidt fight briefly and Schmidt removes his human mask to reveal a crimson skull-like face, the effect of the serum on him. The reason he is called the Red Skull. Schmidt and Zola escape before the whole complex collapses, but that is uncertain for either Cap or Bucky.
As Col. Phillips is drafting a press release about Captain America's demise by the enemy, Cap shows up with Bucky and 400 other soldiers, all rescued from Hydra and holding some of their weapons. They hail Captain America as their saviour, and Phillips finally recognizes the true value of Cap.
Back in the States, a woman who kisses him in the mouth corners Cap, infuriating a jealous Peggy.
At Starks’ lab, Rogers picks a shield made of Vibranium, a light-weight rare sound metal that can absorb impacts. And gives Stark ideas on how to configure his uniform.
Cap assembles a team, the Howling Commandos. Bucky is one member. Cap leads them against Hydra bases Cap saw on a map of them during his rescue mission.
When they learn Zola was on a train, they attack it, but it was a trap. During the battle, a side of the train is blasting off, and Bucky falls to his death among the mountains with Rogers not being able to hold his hand.
They capture Zola and lock him in an American prison, where he tells Phillips about Hydra's plans to rule the world.
Cap, the Howling Commandos, Peggy and Phillips army attack the last Hydra base in the Alps. The Red Skull escapes on a plane carrying several atomic bombs but Cap can infiltrate the plane. After defeating the villain’s minions, he comes face to face with the Red Skull. During their fight, they accidentally break the device holding the Cosmic Cube. When the Skull grabs it, he vanishes into the stream of light to the sky. The Cube falls to the ground, burns a hole and drops into the ocean.
Knowing the plane is carrying those bombs and heads to New York City, Cap calls Peggy. He tells her he will bring the plane down in the ocean to save everyone. Peggy tries to dissuade him from sacrificing himself by finding another way, but there is no time. Cap points the plane to the icy waters. Their communication drops after talking about meeting on a date to dance.
In the days that follow, a submarine recovers the Cosmic Cube, but 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. It appears to be 1943, but the baseball game on the radio is from 1941. Rogers breaks out of the room, which was a set, and races through the building out into a Times Square, but it looks utterly unfamiliar to him.
Colonel Nick Fury, who apologizes for the charade, promptly met him. They merely wanted to make the bad news easier for him to digest… He has been asleep for nearly seventy years. Steve replies "I had a date."
EPILOGUE: After the credits Steve is training in 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.