Eight-year-old Beth Harmon is orphaned when her mother dies in a car crash; she then moves into the Methuen Home in Mount Sterling, Kentucky. Methuen is a strict and tense place for Beth, but she finds respite in the tranquilizers distributed by the orphanage staff to keep the girls calm. Beth also befriends an older girl, Jolene. One day, Beth sees the janitor, Mr. Shaibel, playing chess against himself in the basement. She learns as much as she can by observing him, and over time, he teaches her the pieces, the squares, and different openings and variations. Beth often sneaks out of class and chapel to play with Mr. Shaibel, and she plays in her head while she lies in bed at night. She shows a natural talent for the game and gradually beats Mr. Shaibel consistently. However, when the school stops giving the students tranquilizers, realizing how harmful they are, Beth experiences withdrawal and steals the jar of pills. She is caught after swallowing thirty pills, and though she survives her subsequent hospital stay, the director, Mrs. Deardorff, does not let her play chess anymore.
When Beth is 13, she is adopted by a couple in Lexington, Mr. Wheatley and Mrs. Wheatley. Mr. Wheatley is indifferent to Beth and is often away on business, while Mrs. Wheatley is excited to have a daughter but also somewhat distant—she drinks and gets sick frequently. She also takes tranquilizers for her illness, and Beth starts to steal some of her pills. Meanwhile, Beth learns of the Kentucky State Chess Championship and enters the tournament, despite the fact that she is an unrated player. She feels out of place, as most players are men in their 20s, but she is able to beat each person she plays. This includes Townes, a handsome man who placed fifth in the U.S. Open, and Harry Beltik, an arrogant young man who is the Kentucky State Champion. After winning the tournament, Beth then opens a bank account, gets more books to study, and plans further trips to tournaments in nearby states.
Beth continues to win in tournaments for three years, traveling with Mrs. Wheatley to Cincinnati, Houston, and New York. She likes traveling with Mrs. Wheatley, staying in beautiful hotels and seeing local sites. When Beth competes at the U.S. Open at 16 years old, Beth once again sees Townes, who is covering the tournament for a magazine. Beth also meets Benny Watts, the current U.S. Champion. Benny is in his 20s and was considered a prodigy when he was younger. When they meet, he points out an error that she made in her game against Beltik. When she faces Benny in her final match of the tournament, Beth gets so caught up in her own game that she doesn’t see his surprise attack. It is her first major loss, and she is devastated.
Soon after, Beth and Mrs. Wheatley travel to Mexico City for an international tournament. Beth spends much of the trip studying, knowing that she’ll be facing some of her toughest opponents yet, including Vasily Borgov, the World Champion. She also notices over the trip that Mrs. Wheatley seems very lethargic and sick. When Beth finally faces Borgov, she goes in with little confidence. She crumbles under the onslaught of his moves and experiences a demoralizing loss. When she returns to her hotel room, she experiences another loss, as she finds Mrs. Wheatley dead in bed. The manager helps Beth sort out arrangements for Mrs. Wheatley, who appears to have died of hepatitis. Beth also buys tons of tranquilizers, for which she does not need a prescription in Mexico. She contacts Mr. Wheatley, who has effectively disappeared from her life and moved to the Southwest, and informs him of the news. He tells her to handle the funeral arrangements and that if she keeps up the mortgage payments, she can have the house.
Back in Kentucky, Beth gives herself a little time to grieve before she receives a phone call. It’s Harry Beltik: he’ll be in Kentucky for the summer, and he offers to help train her so that she can stand up to the Russian players. Beth agrees, and Harry moves into her house with her. They spend grueling weeks studying, playing chess, and also having sex. However, by the end of the weeks, Harry can’t win against Beth, and Beth feels that he has nothing left to teach her. She continues to study on her own as well as drink and take tranquilizers, hoping to beat Benny Watts at the upcoming U.S. Championship. At the U.S. Championship, Beth surprises Benny by trading her queens early in the game and puts him on the defense. Ultimately, she beats him handily, becoming the new U.S. Champion.
After the winners’ ceremony, Benny offers to host her at his apartment in New York to help her prepare for upcoming tournaments in Paris and Moscow, which Beth accepts. They drive together to New York, where Beth discovers Benny’s apartment is quite dingy but with a fully stocked library of chess books. They start rigorous study, focusing particularly on Borgov’s games. Beth starts to beat Benny consistently, even when they play speed chess. One day after several weeks, Benny asks Beth to sleep with him, and she does so. But she gets aggravated with the lack of emotional intimacy between them. They spend the next several days as lovers, but Beth soon leaves for Paris. She knows she’s fond of him, but that’s the extent of their relationship, and she feels that he has little left to teach her.
Beth has never felt more prepared than she does in Paris, and she wins several grueling games before facing Borgov. Despite her study and preparation, however, Borgov still outplays her, and she feels sick and powerless when she loses. She returns to Kentucky to lick her wounds, and when Mr. Wheatley returns, intending to sell the house, she buys it from him. Feeling completely alone, Beth quickly falls into a spiral of alcohol and pills. She barely eats, instead remaining constantly drunk for weeks. She only snaps out of it when the Kentucky State Championship director calls her to remind her about the tournament the next day. She goes, but she quickly realizes how out of shape she is and is set to lose in the first round. Unable to face this humiliation, she drops out, saying she doesn’t feel well.
Beth continues to drink, even though she’s now worried that the drinking has damaged her mind and her talent. She ultimately calls Jolene—now a graduate student at the University of Kentucky—to whom she hasn’t spoken since she left Methuen. Jolene helps Beth exercise, get a better diet, and clean up her home so that she will be less tempted to drink. Meanwhile, a letter arrives from the Christian Crusade, a group that offers to help Beth pay for a trip to Moscow to play in a tournament there. Benny tells her to take their help, because they can also pay for him to accompany her. Beth then attends a tournament in California and is relieved to realize that she can play well again, winning the tournament.
Soon after, Beth learns that Mr. Shaibel has died, and she and Jolene attend his funeral. Beth is touched to learn afterward that Mr. Shaibel continued to follow her career. Later, Beth receives a visit from two women from the Christian Crusade, who remind her of Mrs. Deardorff because of their bullying tactics. When they try to get her to make a statement in support of Christianity, Beth refuses and gives them back their money. Benny is furious; this means he can’t accompany her to Russia because he doesn’t have the money. Beth realizes her mistake and he tells her that he doesn’t want to talk to her anymore.
Beth travels to Russia accompanied by a man from the U.S. State Department, Mr. Booth. Beth is intimidated by the players, but she has been preparing intently for the matches. She makes it to the final, even beating out a former World Champion named Luchenko who tells her that she may be the best player he has ever played. In the final match, Beth faces Borgov, and they play for several hours before having to adjourn. That night, Beth studies the position as best she can, knowing that Borgov has a team of other Russian players helping him sort out different strategies he could use. This is why Beth is thrilled when she receives a phone call from Benny, who has assembled a bunch of other players to help her sort through potential strategies. When she returns to the board, Beth plays a few moves following Benny’s suggestions until Borgov makes an unexpected move. However, Beth is able to take Borgov by surprise in return and Borgov ultimately resigns the game. He gets up and hugs her to tremendous applause. After the match, Beth wanders away from the party celebrating the championship and ends up in a park where a bunch of old Russian men are sitting at chess tables and playing. She asks a man sitting alone at one of the boards to play.