Inside a creepy, Southern Gothic New Orleans mansion, another aging Dixie aristocratic similar to—but even more significantly different from—Blanche DuBois is meeting Dr. Cukrowicz. Mrs. Violet Venable is attempting to talk the physician into lobotomizing her niece, Catharine. The legacy of Southern families was unalterably tarnished by the specter of slavery whether one owned human beings or not and thus a tendency arose to protect what remains of the reputation of those families at all cost. The cost of protecting the Venable family name from the ravages of a sordid story involving Violet’s son, Sebastian, is well worth the cost of a portion of Catharine’s brain. At least to Violet. The doctor, however, remains less the fully convinced.
Catharine and her nurse have an argument about Catharine’s smoking habit outside while the physician—whom has instructed his patient to call him “Dr. Sugar”—watches them from afar. Catharine spots him and cries out the name of the hospital which is being used as bait by her Aunt to secure her own lobotomy. This is her way of letting Dr. Sugar she knows the score.
Catharine’s mother and brother arrive in an attempt to convince her not to upset the economic applecart with her bizarre stories of what happened to Sebastian last summer. Catharine, however, as always, never varies from a single detail in her tale of horror.
Catharine’s family is still fighting for her inheritance while the Violet and Catharine’s mother fight over who has the right to allow Dr. Sugar to perform his lobotomy. The doctor learns from Catharine of Sebastian Venable’s homosexuality as well as her own promiscuity. She finally decides to deliver the full goods on exactly what happened suddenly last summer when she collapses into the doctor’s arms, having grown dizzy from the drugs being pumped into her. When her brother, mother, and attendant nursing nun from the mental hospital listen on, Dr. Sugar convinces Catharine to tell the whole truth. They listen in horror to Catharine’s bizarre and seemingly unlikely tale of Sebastian Venable using the remarkably attractive form of his cousin wearing a see-through swimsuit to attract men for his own homosexual lust that ultimately ends with a swarm of young men engaging in a quite literal cannibalistic feeding frenzy of Sebastian's body. When Violet orders Dr. Sugar to cut this hideous story from her brain, he moves much closer to accepting that Catharine has made up nothing.