Warning: Wikipedia contains spoilers
During her lunch break, Polly Parrish (Rogers), an attractive and sympathetic salesgirl at Merlin's Department Store in New York who has just been told that she is going to be dismissed, witnesses a stranger leaving her newborn baby on the steps of an orphanage. Unable to follow her in the busy street crowded with Christmas shoppers, she rings the bell of the orphanage and wants to put the boy in their care. But they are not prepared to take him up, and Polly soon finds out that no one believes her when she says that the baby is not hers. Rather than ostracizing her as a single mother, J.B. Merlin (Coburn), who has been informed of her allegedly illegitimate child by the orphanage, is willing to give her back her job and support her as best he can. Also Polly's landlady is very sympathetic and offers to take care of the boy when Polly is at work. In the end, she gives in and starts raising the child.
J.B. Merlin has a soft spot for children, having been waiting for a long time for his playboy son David (Niven) to produce a grandson. When David and Polly meet at the toy department of Merlin's Store, it is not easy for them to confess both to one another and themselves that they have fallen in love with each other: On the one hand, there is the gap between rich and poor which is not easily bridged; on the other, David is shocked when he learns that Polly is the mother of an illegitimate child. Keeping his relationship a secret from his father, he gradually warms to the idea of having a son, and when, on New Year's Eve, he and Polly kiss among the crowds on Times Square, they seal their future as a family. Through some indiscretion, J.B. Merlin thinks he knows that David is the father of Polly's child, and is only too willing to believe it. In the end, the young orphan is de facto adopted by Mr & Mrs David Merlin.