Wealthy young socialite Judith "Judy" Traherne spends her time partying and horse riding. She has many friends but no one really close, except for her cousin Ann, who serves as her companion. But Judy is hiding symptoms which are rapidly becoming worse. For several months she has headaches and memory loss. Then her vision becomes affected. Trying to laugh it off, Judy confides in Ann. But Ann takes it seriously, especially after Judy is injured in a horse riding accident. Dr. Parsons, the family's elderly physician, believes her to be seriously ill. He recommends that she see Dr. Frederick Steele, a neurologist. Judy refuses until she falls down the stairs. Reluctantly, she agrees to at least meet Dr. Steele.
Although Dr. Steele is closing his office to move to Vermont and do research, he makes time to see Judy. She is flippant until he asks her why she is so afraid. Whatever is wrong won't go away by ignoring it. He asks about her symptoms, which she tries to dismiss but finally admits to having. After performing a few simple tests in his office, he wants her to have a series of x-rays. Between these appointments, she is to go about her life as usual. For Judy, that means giving a party at her home.
Dr. Steele calls in two other neurologists to look at the x-rays and all agree that Judy needs immediate surgery. By this time, Dr. Steele is in love with Judy, although he manages to hide it. He is certain that surgery will reveal a malignant brain tumor, a glioma, and this proves to be the case. But he tells her she will be fine now, not wising to upset her by telling the truth. Ann senses he is holding something back and at last he tells her. They both agree that Judy should not know, even though she only has a few months left to live. Frederick reveals that she won't be in any pain, and that when she starts losing her eyesight, the end is near.
Frederick and Judy admit their feelings for each other and make plans to marry. Judy visits Frederick's office while his nurse is packing for the move to Vermont. She catches sight of a file folder with her name on it and can't resist peeking. To her horror, she learns that her case is considered "prognosis, negative" and asks the nurse what it means. After learning that it means the patient is likely dying, Judy runs from the office and confronts Frederick. He tries to explain but there is really nothing to say. She thinks he wants to marry her out of pity. They quarrel and Judy returns to her old life of partying and drinking. Her horse trainer, Michael O'Leary, who is secretly in love with her, kisses her and asks her to forget Dr. Steele. But Judy realizes she can never forget Frederick.
One of Judy's more serious boyfriends, playboy Alec, invites Frederick to his apartment for a drink. They discuss Judy. Alec has loved her for years but he can't help her now. Just then the bell rings and it is Judy. She came to talk to Alec and is startled to see Frederick. Alec tactfully excuses himself, Judy apologizes, and Frederick says there is nothing to apologize for. They decide to carry out their original plan, to marry and move to Vermont.
Three months later, Judy is still feeling well and is very happy in her marriage. Ann comes for a visit. She is trying to sell Judy's apartment and horses, but so far hasn't found a buyer. Frederick has a chance to speak with Ann alone and warns her not to say anything to Judy about her terminal condition. They never discuss it and he doesn't want it brought up now.
During Ann's visit, Michael the horse trainer stops by. Judy reminds him that her horse should win the upcoming Grand National, even though he doesn't think so. He tells her he's been praying for her, which seems to displease her.
Frederick is going to a medical conference in New York and Judy is expecting to go with him. But while outside helping Ann plant flower bulbs, she remarks that a storm must be brewing, as it's getting dark. Ann instantly knows what is happening, and Judy realizes it too. She orders Ann to say nothing to Frederick, that he must make this trip because it is important for his research. They go inside and Judy tells Frederick that she's changed her mind about accompanying him. Although nearly blind, she manages to conceal this from him and even helps him finish packing. After he departs, Judy asks Ann to help her plant the hyacinth bulbs, as they are Frederick's favorite. Ann digs the holes and Judy plants several bulbs. She asks Ann to always stay with Frederick, as he will be so lonely. If Judy's horse wins the Grand National, Ann is to give a big party for all their friends and serve champagne. Then Judy asks to go inside. At the door, she says that she wants to be alone and asks Ann to leave for a while. Ann runs off down the road, unable to hold back her tears.
The housekeeper, Martha, checks on Judy and find her kneeling in prayer beside her bed. Then she lies down. Martha covers her with a duvet and quietly leaves the room. The last scene is of Judy awaiting death.