During World War II, Ellen Jones Loretta Young works as a nurse in a naval hospital. While dating Lieutenant Ranney Grahame Bruce Cowling, a busy military doctor with little time for romance, Ellen meets Ranney's friend George Z. Jones Barry Sullivan, a pilot. Ellen falls deeply in love with George and marries him after leaving Ranney on amicable terms. When the war ends, Ellen and George move into a suburban Los Angeles neighborhood.
Years later, not all is well with the young couple. George has proven to be selfish, petty, and domineering, and Ellen feels unfulfilled because they have yet to have any children. Despite this, Ellen still loves her husband, and when he begins suffering heart problems, she tirelessly cares for him with the help of Ranney, who periodically visits in his capacity as George's personal physician. During a heat wave, George's illness is exacerbated and he is bedridden. He also becomes increasingly delusional, to the point that Ranney concludes he needs psychological help.
George begins suspecting that Ellen and Ranney are having an affair, and that Ellen is trying to kill him by giving him overdoses of his heart medication. He writes a letter to the district attorney accusing Ellen and Ranney of conspiring to murder him, then gives the letter to Ellen to send in the mail, thinking it is correspondence with their insurance company. Ellen dutifully hands the letter to the postman, and a sense of dread gnaws at her as she contemplates the consequences. When Ellen returns to George's room, she finds him out of bed and manic. He informs his wife of the letter's contents and then brandishes a gun at her, declaring that he has arranged the situation so that he can shoot her and justify it as self-defense. Before George can pull the trigger, however, he collapses on the bed and dies.
Realizing that George's letter could still frame her as his murderer, Ellen rushes out of the house to retrieve it, but obstacle after obstacle gets in her way. She catches up to the postman Mr. Carston only for him to insist that George must request the letter be returned himself, otherwise Ellen must take the issue up with the supervisor of the local post office before the letter is sent out for delivery. Meanwhile, George's snobbish aunt Clara arrives at the Jones residence to visit George, and lets herself in the locked home without permission. Ellen manages to return in time to prevent Clara from entering George's bedroom and finding his body, and after some hysterics persuades her to leave. After tidying up her disheveled appearance in preparation for visiting the post office, Ellen then notices the gun still in George's hand and decides to remove and hide it. It fires a bullet into the floor while the room's window is open but only the neighbor boy Brad Morrow hears, which Ellen misrepresents to him as a radio Western. Then a notary arrives for an appointment with George but Ellen sends him away by insisting her husband is too ill to see visitors. As Ellen departs by car, in her haste, she narrowly avoids running over Billy.
Finally, at the post office, the supervisor is at first sympathetic and gives Ellen a form, that in order to reclaim the letter, must be signed by George. By this point, Ellen is so frantic and desperate that her behavior irks the supervisor and he decides to send the letter out regardless.
Ellen returns home, defeated. When Ranney arrives to check on George's condition, he calms Ellen and enters the bedroom where he takes stock of his dead friend, the bullet hole in the floor and the gun in the dresser. After repositioning George's body and covering it with a sheet, he allows Ellen to explain what happened. When she is finished with her tale, the doorbell rings. Ellen despairs, believing the police have come to arrest her but, at Ranney's urging, opens the door. She finds the postman has come to return George's letter due to it having insufficient postage. Ellen is overcome with relief and Ranney tears up the letter and burns the pieces.
