At the end of World War II, Fred Derry (Dana Andrews), Al Stevenson (Fredric March) and Homer Parrish (Harold Russell) return home to Boone City. Fred was a decorated captain in the Army Air Forces in Europe, Al a sergeant in the Army who saw action in the Pacific, and Homer a sailor who served on an aircraft carrier in the Pacific. Homer's ship was sunk, killing many of his fellow sailors; his arms were burned off below the elbow and he now uses metal hook prostheses. The three men share first a plane trip then a cab ride and become friends. Although he rose to the rank of captain, Fred was an unskilled soda jerk before the war, while the older Al was a bank executive. Homer was a star athlete engaged to be married to the girl next door, Wilma (Cathy O'Donnell). Aware of how uncomfortable his hooks make people, Homer begins to pull away from Wilma and his family. He feels comfortable only when he is with Al and Fred or hanging out with his Uncle Butch (Hoagy Carmichael), who owns a comfortable tavern.
Fred is married to Marie (Virginia Mayo) but can't find her when he returns home, as she has begun to work nights at one of Boone City's night clubs. Al struggles to readjust to family life. His wife, Milly (Myrna Loy) and daughter, Peggy (Theresa Wright), do their best to make him comfortable, but he develops a drinking problem. On his first night home, he insists they go out drinking. At Butch's, they run into Fred and Homer, who has come there to get away from Wilma. Al and Fred get extremely drunk.
When Fred passes out in front of Marie's apartment building, Peggy and Milly take him home with them. The next morning, Peggy drives Fred to Marie's building. On the way, they struggle with the fact they are attracted to one another. Al is promoted at the bank. He is now in charge of approving loans to servicemen under the GI Bill. He believes in taking risks on the servicemen even if they don't have any collaterol for loans. Although the director of the bank gently upbraids him in private, he applauds Al's slightly drunken public speech that providing the servicemen loans is tantamount to investing in the country's future.
Al knows the bank will continue to question his loan approvals. Fred and Marie initially do well upon his return, when he still has money he earned in the Air Force. But when it runs out, he is forced to return to his job as a soda jerk. This angers Marie, who wants to be married to a dashing, successful, rich military man. Peggy visits Fred at the drug store, and they have lunch together.
Afterwards, they kiss. That night, Peggy phones Marie and asks her and Fred out on a double date with a man she is uninterested in. Peggy despises the way Marie speaks of Fred and resolves to break up their marriage. When she tells this to Al and Milly, they tell her that all marriages struggle and that she should leave Fred and Marie alone.
The next day, Al orders Fred to never see Peggy again. Fred calls Peggy to break things off, devestating her. Homer continues to isolate himself. Late one night, Wilma comes over and tells him that her parents want her to break off their engagement, though she doesn't want to. He takes her to his room to show her how difficult life will be with him: removing his prostheses, he shows her that he is unable to button his pajamas or even open a door. Tenderly, Wilma buttons his pajamas and tells him that she loves him and will never leave him. Homer finally accepts that people will accept him.
Fred is fired from his job when he punches out a man who had told Homer that he and anyone else who died in the war were suckers who fought on the wrong side. Marie takes up with a successful serviceman and announces her intention of divorcing Fred. Disillusioned, Fred decides to leave town for good, leaving behind the medals and citations he won during the war. While waiting for an Army transport plane out of town, he reminisces inside a decommissioned bomber like the one he flew over Europe.
When the foreman of the company dismantling the planes tells him the metal will be used to build new houses, Fred talks him into a job. Fred is best man at Homer's wedding to Wilma. He sees Fred for the first time since being ordered to leave Peggy alone. After the ceremony, Fred and Peggy embrace. He tells her that life with him will be hard as he doesn't have much money. She smiles and kisses him.