In New York City, Ruth Wood [Jane Wyman] works as a secretary for Excelsior Shoe Manufacturing Company and lives with her elderly mother, Agnes Wood [Josephine Hutchinson]. Ruth's co-workers are Grace Ullman [Eileen Heckart] and Millie Kranz [Peggie Castle], who is having an affair with her married boss, Stephen Jalonik [Fred Clark]. One evening after work, Arthur Hugenon [Van Johnson], a G.I. stationed nearby, starts a conversation. On her bus ride home, Arthur invites her to dinner but she declines, stating her mother is expecting her. Undeterred, Arthur buys food from a local delicatessen and accompanies Ruth home.
Agnes, who has distrusted men since her husband Harry Wood [William Gargan] left her ten years earlier, receives Arthur with little enthusiasm. After dinner, Arthur finds an unfinished melody Harry had composed, by a piano. He asks permission for him and Dixie Dooley [Paul Smith], his war buddy, to write lyrics for it. Later, that weekend, Arthur accompanies Ruth and Grace for the evening. After passing by an auction, Ruth impulsively bids on an antique Roman coin, which she gives to Arthur for good luck. Afterwards, they attend a French restaurant, where Ruth is unaware that the piano player is her father, whom she has not seen since he left Agnes. However, Harry recognizes Ruth and confides to his bartender friend Andy that he is too ashamed to return to his family.
The next day, Arthur arrives late for their date, but brings the revised song entitled I’ll Always Believe in You, which he sings together with Ruth. As they walk around Central Park, Ruth voices fears about the war, but Arthur tells her she must have faith. They then encounter Sergeant Gil Parker, who asks Arthur to take pictures of him and his new singer bride, Arlene Witchy [Barbara Nichols]. Gil soon photographs Arthur and Ruth together. In private, Gil warns Arthur that his division are to be shipped overseas, but Arthur refuses to believe the rumor.
At the lagoon, where children are sailing toy boats, Arthur recognizes Commodore Eli B. Windgate, nicknamed "Windy" [Halliwell Hobbes]. Hoping to be a reporter after the war, Arthur goes with Ruth to The New York Times Building and convinces the editor to let him write a human interest story, with Windgate as the subject. The story is published but instead of being paid, Arthur asks to be considered for a job after the war. Sometime later, Arthur informs Ruth he has been deployed overseas but vows to marry Ruth when he returns. He soon leaves on a truck filled with other soldiers, and takes with him the Roman coin.
For three months, Ruth writes to Arthur but receives no letter in response. A mailman hands Ruth a letter informing her that Arthur had died in combat. Ruth falls into a depression, which causes Millie Kranz [Peggie Castle] to leave Jalonik and the firm. Grace takes Ruth to St. Patrick's Cathedral, where Ruth continually returns to pray under the statue of Saint Andrew. There, she converses with the cathedral's young priest [Paul Picerni].
Losing interest in life, Ruth's condition worsens into pneumonia. Mrs. Hamer [Irene Seidner], the upstairs neighbor who attends to Agnes, helps to nurse Ruth. One rainy night, Ruth leaves the apartment while Harry Wood contemplates walking in to ask Agnes for forgiveness. Stunned at seeing him, Agnes also realizes that Ruth is missing, just as Grace telephones. After being told that Ruth has left, Grace realizes that she must be heading for the cathedral.
Standing on the cathedral steps, Ruth hears Arthur's voice calling her name. Delirious, she sees Arthur materialize and they embrace as he states their love will never die. He returns the Roman coin, and within a moment, the priest finds Ruth unconscious on the steps, just as Grace arrives. Grace recognizes the coin clasped in Ruth's hand, and realizes that Arthur had returned to Ruth, whose life remains clouded in uncertainty.
