In the present day, scientists in the Arctic discover a frozen aircraft with a person inside and a mysterious circular shield. Flashing back to March 1942, during World War II, Nazi lieutenant general Johann Schmidt steals a powerful relic called the Tesseract from the town of Tønsberg in German-occupied Norway. The Tesseract holds immense power, which Schmidt and Dr. Arnim Zola plan to use to fuel their weapons and alter the course of the war.

In New York City, Steve Rogers is initially rejected for U.S. Army enlistment due to his health issues but later accepted into the Strategic Scientific Reserve for a super-soldier experiment led by Dr. Abraham Erskine, Colonel Chester Phillips, and British MI6 agent Peggy Carter. Despite skepticism from Phillips, Rogers proves himself worthy by jumping on a grenade during a test. Erskine reveals that Schmidt had stolen his prototype formula, becoming superhuman with adverse effects. Erskine administers the formula to Rogers, transforming him into a super-soldier, but is killed by an assassin sent by Schmidt, who steals a vial of the serum.

Rogers, now Captain America, is initially used for war bond promotions while scientists attempt to replicate the super-soldier formula. When he learns that his friend Bucky Barnes’ unit is missing in action, Rogers leads a solo rescue mission, saving Barnes and others from Schmidt’s Hydra division. Schmidt, now known as the Red Skull due to his exposure to the Tesseract, escapes, and Rogers assembles a team to attack Hydra bases. Stark equips Rogers with advanced gear, including a vibranium shield.

In 1945, Captain America and his team attack a train carrying Hydra scientist Dr. Zola. Although they capture Zola, Barnes falls from the train and is presumed dead. Rogers leads the final assault on Schmidt’s stronghold and boards Schmidt’s super-bomber, The Valkyrie, to prevent him from using his weapons of mass destruction. During the battle, Schmidt is sucked into a portal after handling the Tesseract, which is lost in the ocean. Rogers crashes the plane in the Arctic to avoid a catastrophic explosion, and is presumed dead by Stark, who later recovers the Tesseract.

Rogers wakes up in a present-day hospital room, confused by the modern world and a radio broadcast of a baseball game he attended in 1941. He discovers he has been “asleep” for nearly 70 years. S.H.I.E.L.D. director Nick Fury informs him of his long absence and proposes a mission with global implications.