The story of The Only Girl tells of four friends who have determined to remain bachelors. One by one they get married to the only girl. Only one of the four is left. He is a librettist, seeking a composer who will write an opera for him. Hearing an exquisite melody from the apartment above, he sends for the musician. Though his surprise the composer proves to be a beautiful young woman. As he dislikes women heartily, he is greatly disappointed, but finally concludes to treat her in an impersonal fashion, asking her to do the same. So they work together like two machines until at the close of the play he joins the benedicts. His three friends and their brides form an amusing part of the plot.