On 1 June 1942, meek bank clerk Wilbert Winkle screws up his courage and informs his boss, bank president A. B. Simkins, that he is quitting after fourteen years of service. When Simkins angrily accepts his resignation, Winkle's brother-in-law, Ralph Wescott, who is also employed at the bank, phones his sister Amy, Winkle's wife, to tell her the news. After leaving the office, Winkle visits Barry, an orphan he has befriended, and accompanies the boy to his workshop, which is situated behind the Winkle house. Telling Barry that he has designated the first of June as the day to open his fix-it-shop, Winkle asks the boy to join the business as a handy man. When Winkle informs the domineering Amy about his new venture, she declares that she will not be humiliated by being married to a handy man and demands that he choose between her and his shop. Ignoring Amy's threats, Winkle goes to work at the shop with Barry the next day. Late in the afternoon, the mailman delivers an induction notice to the Winkle house, and Amy takes the letter to her husband at his workshop. The next morning, Winkle reports to the induction center where, to his surprise, he is orderd to report to duty immediately. After the first day of grueling basic training, Winkle's commanding officer, Sgt. "Alphabet," decides to reassign the sickly recruit to a desk job. When Winkle pleads to be allowed to serve his country by using his mechanical abilities, the sergeant finally agrees to transfer him to a mechanical division. After undergoing a strenuous training program, Winkle is transformed into a robust soldier and is assigned to the motor mechanic unit. On the eve of his first furlough home, he is summoned back to the post to be shipped overseas to a combat area. As Winkle prepares to join his unit, his commanding officer informs him of a new army regulation granting an honorable discharge to all men over thirty-eight. Although Winkle is forty-four, he turns down the discharge to serve his country and phones Barry to tell him that he will not be coming home. Bitterly disappointed, Barry runs away to see Winkle, and when Mr. McDavid, the head of the orphanage, learns of the boy's plans, he and Amy go looking for him. After they find him hitchhiking along the road, Barry tells Amy that Winkle will not be coming home. When Amy wonders why her husband didn't accept a discharge, Barry rebukes her for failing to appreciate Winkle's integrity. That night, Winkle is shipped out to a Pacific island, where he is ordered to repair a broken-down bulldozer. While he is working on the engine, a contingent of Japanese soldiers attack Winkle's platoon. Although he is in the thick of gunfire, Winkle refuses to give up and continues to tinker with the engine until it finally starts. Driving the vehicle toward the enemy soldiers, Winkle overruns their position and routs their attack. Wounded in combat, he awakens in a hospital bed to discover that he has been declared a hero. Upon returning home, the modest Winkle avoids a welcoming reception and goes straight home, where Amy is waiting. When the crowd finds him there, Simkins announces that Winkle has been appointed vice-president of the bank. After Winkle rejects the promotion, Amy, who has finally accepted her husband's humble desire to work in a fix-it shop, escorts him to the back porch and shows him the short cut to his shop that she and Barry have built through the back fence.