In New Orleans during the summer, newly married Stella Dubois, now Mrs. Stanley Kowalski, receives a visit from her older sister, Blanche. Blanche coyly says she doesn't want to be a burden and that she knows Stella wants her to go to a hotel, but she wants to be closer to Stella. She also comments on Stella's lowly living conditions, but Stella assures her she's happy. Blanche tells Stella she has lost their family's plantation and resigned from her position as a schoolteacher.
Upset, Stella goes into the bathroom to freshen up. Meanwhile, her husband Stan comes home and Blanche introduces herself. They make small talk and Blanche appears nervous. The next day, Stan finds out from Stella before his weekly poker game that Blanche has lost the family plantation. He goes through her things and pulls out all the nice dresses and jewelry, believing Blanche has defrauded the family for her own riches. However, Stella assures him her possessions are not real, particularly the tiara which has rhinestones not diamonds, which are "next to glass." Stella asks Stan to make Blanche feel good about her appearance and not to mention that they are expecting a baby.
When Blanche comes out from her bath and Stella has left, Stan and Blanche have a conversation about the plantation. He demands to see her papers detailing what happened to the plantation, and she pulls out a small box containing them to show him. He also grabs some love letters from the box and Blanche becomes distraught, declaring that his touch has tainted them. She tells him the papers detail that the plantation, once of great value, was traded down to nothing because of her ancestors not through her own fault.
Later, at the poker game, Blanche meets Mitch, one of Stan's friends who is single and lives with his sick mother. The two become enamored instantly. While Blanche and Stella listen to music and laugh, Stan becomes upset they are disrupting his game and throws the radio out the window. When Stella scolds him, he corners her in the kitchen and hits her. Stella and Blanche go to Eunice's apartment above them, but Stella soon returns to Stan and the two go back to the bedroom to make up. Mitch assures Blanche this is normal and they are crazy about each other.
The next morning Blanche, in a frenzy of worry, tries to convince Stella they need to get some money and run away. She has a rich friend who will be able to help them, but Stella does not want to leave Stan and is upset at Blanche acting superior. Stan arrives at the house and overhears their conversation, unbeknownst to Blanche who is telling Stella he is "common" and she should leave him.