This sentimental film about World War II was made ten years after the war ended. It opens in 1942, when timid Ruth Wood (Jane Wyman) is accosted by boisterous GI Art Hugenon (Van Johnson) on the street. Despite her protestations, he cheekily invites himself to dinner with her and her mother. Ruth's mother is in a state of permanent depression. Years ago, her husband left her for another woman and abandoned her and Ruth. She's held a grudge against men ever since, even though she's carefully preserved all her husband's possessions and continues to carefully mend the clothing he left behind. She definitely has issues. Needless to say, she cowers at the sight of Art. Art makes her even more miserable when he finds some music her musician husband wrote before he left. Art sits down at the piano and plays it and starts to make up words to go with the music. Ruth's mother is terrified that Ruth will abandon her the same way her husband did. We can see the kind of pressure Ruth is under to please her mother and how desolate her life was before she met Art.
Art and Ruth have a whirlwind courtship that consists of enjoying the city. They go to an auction and Ruth buys Art a supposedly old Roman coin for two dollars. Art says he'll punch a hole in it and wear it around his neck to remind him of her. Art loves New York, and after the war he wants to move to the city and be a reporter for the New York Times. He even manages to sell the paper a story about a down and out, once famous and wealthy, boat designer he and Ruth meet in Central Park. They also have dinner at a French restaurant where Ruth's dad (unbeknownst to her) plays the piano for the diners. Her father recognizes her, laments his failures as a husband and father to the bartender, and his ultimate response is to knock down some drinks at the bar and then creep out the door.
As to be expected, Art's unit is called overseas. He and Ruth have an emotional farewell. Art asks Ruth to marry him and gives her his mother's engagement ring. Considering how emotionally neglected Ruth has been her whole life, this is earthshaking. She gets a scrapbook with his name embossed on it and carefully cuts out his article from the Times and pastes it in. She writes him every day, but he never writes back. Then, she gets a letter from one of his Army buddies. Art has died in combat and his last words were of his love for Ruth. Ruth is heartbroken naturally, and she goes off the deep end into strange behavior and a crippling depression.
Her friend Agnes takes her St. Patrick's Cathedral to see if sitting quietly in the church will help her come out of her grief. Instead it makes Ruth's behavior even stranger. Ruth (who's not Catholic) becomes obsessed with lighting candles and putting them directly in front of a statue of St. Andrew so that he won't be "alone in the dark." A young priest tries to help her, but to no avail. Ruth's also coughing all the time, she's starting to get sick. Her sleazy, womanizing boss takes her out to the same French restaurant she went to with Art and tries to hit on her. Her dad is there to play the piano, but he turns on the radio and hears the music he wrote at home (and now including Art's words) being played. Art had had a musician friend Dixie Dooley and he innocently gave Dixie the music to evaluate before he went overseas. Ruth's dad figures his wife must have sold the composition and, despite all the years he's spent away from her, casually decides to call her on the phone. He doesn't see Ruth. She leaves her creepy boss and walks out of the restaurant while he's in the phone booth. A coward again, he hangs up when his wife answers the phone.
Now Ruth is really sick. She has pneumonia. Her mom actually comes to life and starts to take care of her daughter instead of her usual moping around their shabby apartment. Ruth's mother falls asleep on the divan in the living room and Ruth climbs out of her sickbed and walks out into into the rainy New York night. Her father, who has been lurking around the building trying to work up the courage to see his wife, doesn't see her. He finally makes it upstairs to the apartment and apologizes to Ruth's mother for what a heel he's been. Ruth's mother comes to her senses (somewhat) and then realizes Ruth is gone. She shrieks to her husband that he must find Ruth. He leaves to find her.
Ruth wanders in the rain to St. Patrick's. In her delirium, she sees Art. He bounds across Fifth Avenue and gives her a hug and tells her he loves her. It's a genuinely affecting scene. He presses the chain with the Roman coin on it into her hand, reaffirms his love, explains that he had not been able to write to her, and says he has to go. She collapses on the steps of the church, alone in the rain. The priest and an altar boy find her. Agnes shows up too. They notice something in her hand. It's the chain with the coin on it. Agnes exclaims that Art took wore it when he went overseas and she can't understand how Ruth has it now. That's the miracle in the rain the film's title refers to.
The movie basically ends with Ruth on the floor in the vestibule of the church attended by the priest and Agnes, waiting for the ambulance to arrive. The curious viewer is left with the open question as to whether or not Ruth actually survived her pneumonia considering that the story was set in 1942.