On a spring day in Chicago, at the turn of the twentieth century, Andrew Delby Larkin, a salesman at Otto Oberkugen's music shop, eagerly rushes to the post office in the hope of finding a letter from his secret pen pal, whom he knows only as "Box Number 237." To Andrew's delight, a letter awaits him, and he proudly reads it to his friend and co-worker, Rudy Hansen. By a strange coincidence, Veronica Fisher, who is Box Number 237, enters Oberkugen's shop that day looking for work, unaware that Andrew is her pen pal. Veronica is met with Andrew's condescending disinterest, as he, too, is unaware that his secret pen pal is in his presence. Mr. Oberkugen at first refuses to hire Veronica, but he eventually offers her a sales position when she cleverly persuades a customer to buy one of his pet instruments, an expensive Amboy harp. Veronica's early success at salesmanship proves to a fluke, however, and sales at the store begin to slide. So, too, does her professional relationship with Andrew, who has become increasingly hostile towards her. On the day that Veronica and Andrew are to meet their respective pen pals, the two arrive at work in high spirits, but their mood quickly changes as they become embroiled in a petty dispute. Furthermore, Oberkugen, who is upset at having been spurned by his sweetheart, employee Nellie Burke, angers both Veronica and Andrew when he orders the entire staff to remain after hours to take a store inventory. Oberkugen eventually has a change of heart, though, and lets his employees out just in time for Andrew and Veronica to rush to their pen pals. When Andrew peers into the restaurant where he is to meet his secret pen pal, he is shocked to discover that his pen pal is Veronica. Bewildered and embarrassed, Andrew runs away before Veronica sees him, and instead goes to a recital by Louise Parkson, one of the residents at the boardinghouse where he lives. Although Andrew eventually changes his mind and returns to the restaurant, he does not reveal to Veronica that he is the person she has been waiting to meet. Instead, he makes a clumsy attempt to win Veronica's affection by flirting with her. This leads to an argument and ends with Veronica leaving the restaurant thinking that her secret pen pal decided not to approach her after having seen her. Devastated by the apparent rejection, Veronica becomes reclusive and refuses to leave her home. Guilt-ridden about what has happened, Andrew asks Veronica to accompany him to Otto and Nellie's engagement party, and she accepts. Later, when Otto learns that Andrew has loaned his prized Stradivarius violin to Louise for her big recital, he fires him. The decision is eventually reversed, though, when Otto realizes that Andrew acted out of kindness, and he is offered his job back with a raise. Having finally secured the pay raise he felt he needed to marry his sweetheart, on Christmas Eve, Andrew reveals to Veronica that he is her secret pen pal. They kiss, and she consents to marry him.