Today, arctic scientists find an ancient, frozen airplane with a frozen person aboard. A mysterious artifact known as the Tesseract, endowed with unfathomable heavenly powers, is taken by Nazi lieutenant general Johann Schmidt and his soldiers from the town of Tønsberg in German-occupied Norway in March 1942 during World War II.
Due to his numerous medical issues, Steve Rogers was turned down for enlistment in the US Army in New York City. Rogers tries to enlist once more as he and his best friend, Sgt. James "Bucky" Barnes, is at an exhibition of future technologies. Dr. Abraham Erskine permits Rogers to enroll after overhearing Rogers' discussion with Barnes over fighting for his nation in the war.
As a "super-soldier" experiment, he is enlisted in the Strategic Scientific Reserve under the direction of Erskine, Colonel Chester Phillips, and British MI6 operative Peggy Carter. Erskine tries to convince Phillips that Rogers is the best candidate for the surgery, but Phillips gives up after witnessing Rogers, not realizing it's a test, jump on a grenade to save his friends. Erskine tells Rogers the night before the procedure that Schmidt used his "early" formula on himself to become stronger, but the results left him with long-lasting adverse effects.
Schmidt and Dr. Arnim Zola capture the Tesseract's energy to use it to power Zola's technologies and launch a global offensive. When Schmidt learns where Erskine is, he sends assassin Heinz Kruger—posing as State Department official Fred Clemson—to take his life. Rogers receives the super-soldier treatment from Erskine, who gives him "vita-rays" and a special serum injection. An undercover Kruger murders Erskine and makes off with a bottle of the serum as Rogers becomes taller and more muscular after the experiment. Rogers tracks down and apprehends Kruger, but before being questioned, the assassin takes a cyanide capsule to end his life.
After Erskine's death and the loss of his super-soldier formula, U.S. Senator Brandt arranges for Rogers to tour the country as “Captain America”. At the same time, scientists research his blood and try to figure out how to reverse-engineer the formula. When Barnes' battalion goes missing in action against Schmidt's forces in 1943, Rogers finds out while on tour in Italy entertaining active personnel. Rogers, not willing to accept Barnes' death, has Carter and engineer Howard Stark fly him behind enemy lines in an attempt to mount a lone rescue. Rogers liberates Barnes and the other detainees by breaking inside Schmidt's Hydra division stronghold. Rogers approaches Schmidt, who takes off a mask to show a red face resembling a skull, earning him the nickname "the Red Skull". Rogers returns to base with the liberated soldiers after Schmidt makes his getaway.
To attack other known Hydra bases, Rogers enlists the help of Barnes, Dum Dum Dugan, Gabe Jones, Jim Morita, James Montgomery Falsworth, and Jacques Dernier. Stark gives Rogers cutting-edge gear, including a circular vibranium shield—a rare, practically unbreakable metal. While he and Carter fall in love, Rogers and his group foil numerous Hydra operations. The group attacks a train that is transporting Zola in 1945. While Barnes appears to have died after falling off the train, Rogers and Jones can apprehend Zola. After discovering the last Hydra stronghold with the help of information taken from Zola, Rogers launches an assault to prevent Schmidt from deploying WMDs on significant American cities.
As the super-bomber The Valkyrie takes off, Rogers boards it. In the ensuing battle, the Tesseract's container sustains damage. When Schmidt touches the Tesseract with his hands, a portal to space opens and he is drawn through. After burning through the aircraft, the Tesseract vanishes into the sea. Rogers radios Carter to bid her farewell before the jet crashes in the Arctic, realizing there is no way to land without running the risk of detonating its weaponry. After the European War is done, Stark finds the Tesseract on the ocean floor and assumes Rogers is dead because he cannot find the aircraft or Rogers.
A hospital room from the 1940s is where Rogers awakens. After hearing a radio broadcast of a 1941 baseball game he attended, Rogers becomes suspicious, runs outside, and ends up at Times Square in the present day. Nick Fury, the head of S.H.I.E.L.D., tells him he has been "asleep" for almost 70 years. During a scene after the credits, Fury approaches Rogers and offers a mission that could have global implications.
