During the early morning watch, Merchant Marine Tom Wingfield remembers his life in a shabby St. Louis apartment with his mother Amanda and crippled sister Laura: Although she must sell magazine subscriptions to supplement Tom's income from his work in a warehouse, Amanda fancies herself to be socially superior to their impoverished neighbors. She blames the family's reduced circumstances on her absent husband, "a telephone operator who fell in love with Long Distance," and abandoned the family years earlier. Afraid that Tom will also leave the family, she nags him to bring home one of his friends to meet, and hopefully court, the shy, lame Laura. At Amanda's urging, Laura is taking a secretarial course, but her only real interest is her collection of small glass animals. Tom dreams of escaping his squalid life and Amanda's romanticized memories of her genteel Southern girlhood. When Amanda learns that Laura has left the secretarial school, she proclaims that they will have to get her married. Laura reminds her mother that she is crippled, and Amanda angrily replies that she must not think of herself that way. One day, Tom invites his friend, Jim O'Connor, to dinner. Carried away by the possibilities of Laura's first "gentleman caller," Amanda imagines Laura married to Jim, and despite Tom's gentle caution that Laura's shyness makes her seem peculiar, Amanda makes elaborate preparations for the dinner. Laura, however, is distressed when she learns the name of their visitor, because she remembers him from high school as one of the most popular boys. She avoids dinner, claiming that she is too ill to eat, but later, when Amanda arranges for Laura to be alone with Jim, his open friendliness draws her out. Diagnosing her shyness as an inferiority complex, Jim persuades her to show him her glass collection and then coaxes her to dance. Laura's awkwardness causes them to accidentally break the horn off Laura's prize glass unicorn. Although she is upset at first, she is able to accept the change because it enables the unicorn to fit in with the horses in the collection. To Amanda's delight, Jim then asks Laura to go across the alley to the Paradise Ballroom. Again Jim encourages Laura to have more self-confidence, and after kissing her, explains that he is engaged to a woman named Betty. Amanda is more upset than Laura, who gives Jim the broken unicorn as a gift and invites him to visit again with Betty. Amanda takes out her disappointment on Tom, who storms out of the apartment. Laura follows him to voice her approval and love. Tom joins the Merchant Marine. Later, Laura has her own gentleman caller.