Joy carefully budgets her limited funds, which have become so tight in recent years that she struggles to afford groceries. She allocates extra money for a special Sunday dinner she is hosting for her daughter, Elizabeth, her grandson, Finn, and Hazel. During her shopping trip in the town of Beacon, she struggles to find parking and has several brief, impersonal interactions with hurried city visitors. In the coffee shop, she gives up the last slice of her favorite lemon cake to a woman who is having a bad day. Outside, she runs into a gossipy acquaintance, Rita, who informs her that a man with a criminal record has moved into a nearby bungalow. The news leaves Joy feeling uneasy.

Hazel arrives several hours early for dinner, having accepted a ride from a stranger at the train station, much to Joy’s concern. When Elizabeth and Finn arrive, Joy observes the warm, easy bond between her daughter and Hazel, which contrasts with the growing distance she feels from Elizabeth. At dinner, Hazel captivates everyone with her adventurous stories. Later, while sitting on the porch, Hazel reveals she has terminal cancer and has refused treatment. She asks Joy not to make a fuss, stating she has lived a full life and is at peace with her impending death. Joy is devastated, realizing she is about to lose her last contemporary and will be left to face the world alone.

The narrative flashes back to 1942 in a small Wisconsin farming town. A second-grader, Joy feels timid and out of place on her first day at a new one-room schoolhouse, having come from Madison. Her father, the town’s only doctor, has instructed her to be on her best behavior. A boy named Billy teases her for her shoes, causing the other students to snicker. Another girl her age, Hazel, immediately defends Joy, telling the room that not everyone is a “sheep.” The confident and charismatic Hazel then persuades the teacher to let Joy sit next to her, initiating their lifelong friendship.

The narrative returns to the present. The morning after Hazel’s cancer revelation, Joy struggles to act normally. To distract themselves, they go shopping in Beacon. Hazel, who is always stylishly dressed, buys several scarves at a vintage boutique. They then visit a secondhand shop owned by Seth, an old acquaintance from New York City. Hazel once again attempts to buy a ceramic vase that has sat on his counter for years, but he refuses to sell it. Joy recalls the vase’s history: It was the last piece made by Hazel’s close friend, an artist named Eric, who died young. Eric repeatedly declined Seth’s offers of representation, and when the vase went to auction, Seth outbid Hazel for it. Hazel suspects he now keeps it from her out of spite.

A week later, Joy is unsettled by Hazel’s morbidly humorous morning text: “Yoo-hoo! I'm not dead yet” (35). After giving a piano lesson to a young girl named Sunny, Joy goes for a walk and meets her new neighbor, Rowan, who is washing his car with his terrier, Hettie, nearby. Rowan is friendly and covered in tattoos. They have a pleasant conversation, and he tells her he is a piano tuner. Despite the positive interaction, Joy remains wary due to Rita’s gossip about his criminal past and makes a mental note to lock her door. She returns home to find smoke billowing and the fire alarm sounding because she forgot about the muffins she put in the oven. She manages to air out the kitchen, grateful that she didn’t start a fire.

Joy attends her weekly board games group at a local church but feels invisible and patronized by the younger members. They treat her condescendingly during a game of UNO, deliberately avoiding playing penalizing cards against her. When she tries to leave, her handbag catches on her chair and spills its contents. Before she can rise from her squat, two young people preemptively take her arms to help her up in front of the whole room, and she feels humiliated.

On the drive home, Joy reflects on her quiet, simple life of raising a child and tending her garden. She compares her own small existence to the adventurous, impactful lives of Hazel and other famous women her age, and for the first time, she wonders what her life might have been like if she had dared to be more rebellious.

In a flashback to 1946, a young Joy takes advantage of her father’s absence to visit her bedridden mother. During these secret meetings, her mother imparts lessons on etiquette and womanhood. She advises Joy to marry a dependable man rather than chase romantic love. She tells Joy to never be an “imposition” on others by sharing her own troubles, as others are likely struggling more. She also instructs Joy to always “button up and smile” (55).

The story shifts back to Joy’s present. Finn arrives at Joy’s home after school feeling dejected. He tells Joy he is being bullied for being a “mommy’s boy” and is hurt that his father, Jack, has canceled their summer visit. To cheer him up, Joy gives him his favorite dessert, her homemade red velvet cupcakes, and takes him to the library. On their way in, they encounter Celeste Hobart, a neighbor Joy dislikes. Inside, Joy sees that a popular book she has on hold is sitting on the shelf, already claimed for the patron ahead of her in the queue. In a sudden, uncharacteristic act of rebellion, she takes the book without checking it out. The security alarm sounds, but the librarian, Max, assumes he forgot to demagnetize one of her legitimate loans and waves her through. Joy is thrilled by the transgression, realizing there is an advantage to being an overlooked old woman.

On the train to New York City, Joy coincidentally sits with her neighbor, Rowan, and his dog. He is so kind and open that Joy finds herself confiding in him about Hazel’s cancer. Rowan is deeply empathetic, revealing that his own mother recently died of cancer. He also tells her he moved to Beacon because he prefers a slower-paced life, and that his long-term partner, Philippe, remains a city dweller, an arrangement they have maintained for about 20 years. As the train passes Sing Sing prison, Rowan shows no reaction, leading Joy to doubt Rita’s gossip about his past. At Grand Central, Joy meets Philippe and is touched by the couple’s affection for each other. The positive encounter gives Joy the confidence to navigate the subway to Hazel’s apartment by herself.

When Joy arrives at Hazel’s Brooklyn loft, she is shocked by her friend’s frail and wasted appearance. Overcome with emotion, Joy bursts into tears, breaking her promise to hide her negative emotions. After they compose themselves, Joy shows Hazel that she’s “made all [her] favorites” (73), such as moussaka and paella, because she knows that her friend struggles to eat now. This generous act reminds Hazel of the care packages that Joy sent to her when she was traveling around the world for her textile business. Hazel asks Joy for a favor: She needs her to meet her marijuana dealer. Hazel explains that she has a medical prescription but finds the dealer’s product more potent than what dispensaries provide. Though shocked and hesitant, Joy agrees because she is desperate to do something to help her friend.

After a nervous wait in a Brooklyn park, Joy meets Hazel’s dealer. He is a polite, clean-cut young man, not the criminal type she had imagined. He gives her a bag containing marijuana and complimentary “mushroom chocolate,” and she pays him, adding a tip. After the seamless transaction, Joy doesn’t feel guilty as she expected. Instead, she feels a “heady rush” and is thrilled by her first real taste of rebellion and the discovery of a bold new side to herself.

The narrative flashes back to Joy’s mother’s funeral in 1947. Standing beside her emotionally stoic father, Joy feels isolated in her grief. As the casket is lowered into the ground, she reaches for her father’s hand, but he remains stiff and unresponsive. Just then, she feels another hand take hers. It is Hazel, who has come to the funeral despite Joy’s father’s disapproval of her. Hazel comforts Joy by squeezing her hand tightly.