The second world war is raging and America needs a hero, especially when faced with Hydra, a force even worse than the Nazis.

The film begins in the present day, when scientists discover a huge plane, frozen in ice. They break into it and discover a frozen body with an iconic shield.

Flashback to 1941, the war against Hitler and his forces is in full swing and a small town in Norway is under siege by Johann Shmitt, the Red Skull. Red Skull breaks into a church run by Argus Filtch and takes a powerful artifact, the Tesseract, that was said to be left behind by Odin.

Meanwhile, in New York, tiny Steve Rodgers tries and fails to qualify for military service for the third or fourth time. He gets into a fight at a movie theater and won’t back down, needing to be rescued by his friend Bucky, who is about to head off to war and decides to take him to the Stark Expo for one final outing. While at the expo Steve gives a passionate speech to Bucky about why he wants to join up so bad, and he decides to try one last time at the Expo’s recruitment center. His speech is overheard by Dr. Erskine, who decides to waive the health requirements and let him enlist for a special program that he is running.

Red Skull takes the Tesseract back to his base and turns it over to Doctor Armin Zola so that he can use the cube’s powers to develop weapons while Steve heads to boot camp, secretly being evaluated for the Super Soldier program. Despite his frail body he manages to impress Dr. Erskine and Agent Peggy Carter and is selected as the first candidate for the program’s procedure. He is told that it will make him strong, and he finds out that one other person has undergone it, although in an early and flawed state: the Red Skull, head of Hitler’s experimental research division Hydra.

Back in New York, Steve undergoes the painful procedure and comes out a new man, at least physically. Unfortunately Hydra has infiltrated the experiment and an agent sets off a bomb in the facility and shoots Dr. Erskine before stealing the last of the serum and bolting. Steve gets acquainted with his new physical abilities as he chases the assailant down, but the serum is lost in the process and the Hydra agent commits suicide. With Erskine and the serum gone Steve will be the only super soldier, and the general decides that one is not enough. He plans to send Steve off to a lab for testing rather than putting him into the field for combat, but a Senator that attended the procedure has another idea, and Steve jumps at a chance to actually serve his country.

For the next several months Steve uses his strength and prowess on stage, becoming a mascot for the military: Captain America. He goes from city to city selling war bonds. The plan is successful, and they raise a decent amount of money, but he realizes his heart isn’t in it. When he heads overseas to perform for the troops he is particularly frustrated. He does run into Agent Carter again, but she can’t help him. She does tell him that he’s doing good work, and that it is benefiting the soldiers. He also learns that Bucky’s division has been decimated by enemy forces, and that most of them are being held captive behind enemy lines. The general confirms that Bucky is most likely dead, and Steve convinces Carter and Howard Stark to help him get past the enemy lines to free the captives.

Cap infiltrates the Hydra weapons factory where the 107’th is being held, busts out the prisoners, and they are able to steal some of the Hydra tech. He finds and rescues Bucky from experiments that they were running on him and the two encounter Red Skull, who reveals that he considers himself to be a super man, and that his face actually is a red skull. Red Skull manages to escape and the factory explodes. The general and Agent Carter assume that Captain America and the others are dead, and Carter is about to be fired for letting him go, but the survivors march into camp victorious and Cap is finally treated as a real soldier. He puts together his own squad, the Howling Commandos, including himself, Bucky, and several of the men that he fought alongside at the factory and the group starts taking out Hydra bases around Europe, while the Red Skull grows more and more furious at the delays Cap is causing to his grand plan. He tosses off the shackles of Nazi Germany, proclaiming Hydra as its own separate entity, and demonstrates the destructive force of his new Tesseract powered weapons in the process.

Cap’s next mission is to capture Doctor Zola, so he leads a small team onto a moving train to corner him. In the process a fight breaks out with Hydra soldiers, and Bucky jumps in the way of a blast meant for Cap, blowing him out of the side of the train and into a deep ravine. Zola is captured, but Cap is devastated by the loss of his friend. Zola, unwilling to commit suicide or wait around for Red Skull to find and kill him, turns over the location of his secret base, and tells them about Red Skulls plan to dominate the world with a giant plane called the Valkyrie.

Cap plans a risky head on assault on the base, intentionally getting himself captured as a distraction to allow the commandos a chance to break in. The assault is going well, but Red Skull manages to break his way through to board the Valkyrie and take off. Steve, with some help from the general and Agent Carter and a fast car, is able to get onto the landing gear and into the plane at the last minute. He fights through more soldiers, and prevents them from launching a few manned bomb planes before making his way to Red Skull on the bridge. Another fight ensues, releasing the Tesseract which is powering the ship. Red Skull grabs the artifact with his bare hands, and it appears to violently teleport him into deep space.

With the plane going down and on a collision course for New York, Cap has no choice other than to crash the plane into an ice shelf. Seventy years later he wakes up in an unfamiliar bed, unknowingly thawed out by SHIELD agents. He quickly pieces together that his surroundings are false and breaks out of their facility and onto the streets of modern day New York. Nick Fury explains what has happened to him, and welcomes him to the new century.

In the post credits Fury approaches Cap in a gym and asks him for help saving the world.

TLDR: Weakling Steve Rodgers desperately wants to join the military, and as a good man is chosen for the Super Soldier program. He becomes an American Icon and fights Nazi’s and Hydra. He puts an end to Hydra’s plans for world domination, but is frozen in ice in the process, only to be thawed out 70 years later.