The film is about a rich industrialist with business problems who feels neglected by his family and hires a young woman to stir things up.

Feeling lonely, Timothy takes the advice of his butler and visits Central Park, where he meets Mary Grey, a young unemployed woman.

The next morning, he wakes with a hangover and a black eye, discovering that he had invited Mary to spend the night in a guest room.

He intentionally neglects his company, thereby forcing his son, Tim who develops fresh new ideas, to save the firm.

Timothy and Mary go out every night, pretending to cavort for hours, although they are actually driven around by the ardently communist chauffeur Mike, whom Katherine loves.

Embarrassed by the newspaper gossip columns and shunned by her friends, Martha consults a psychiatrist who finds nothing wrong with her suddenly cheerful and carefree husband.

[1] The film as presented to preview audiences included a different, unhappy ending with Mary leaving the house and walking down Fifth Avenue.

[2] Fifth Avenue Girl was presented on Lux Radio Theater in 1940, starring Ginger Rogers and Edward Arnold.