Ivy Lin is a thief whose unremarkable appearance allows her to steal without suspicion. Born in Chongqing, China, she is left with her maternal grandmother, Meifeng, when her parents, Nan and Shen Lin, immigrate to Massachusetts. At five, Ivy is sent alone on a plane to join them and her baby brother, Austin. Her parents are strict and emotionally withholding; an incident in which Nan publicly shames six-year-old Ivy for being clingy turns the girl permanently inward and secretive.
Meifeng arrives in the US when Ivy is seven and teaches Ivy self-reliance through shoplifting, price-swapping, and scavenging at yard sales. Ivy becomes a skilled thief, graduating to stealing from big-box stores. She is also a voracious reader who identifies beauty as the source of all desirable traits. When Shen gets a job as a computer technician at Grove Preparatory Day School, Ivy transfers there on free tuition and develops an intense crush on Gideon Speyer, a polished, wealthy classmate she cannot hope to match in status.
Around this time, Ivy befriends Roux Roman, a neighborhood boy who grew up without a father and whose mother has a reputation for promiscuity. They bond as outsiders, but once Ivy transfers to Grove, she distances herself from Roux. When Gideon invites Ivy to his 14th birthday sleepover, she lies to Nan about where she is going. The next morning, the entire Lin family arrives at the Speyers' house to retrieve her, and Ivy overhears classmates mocking her family. At home, Nan discovers Ivy's hidden stash of stolen goods and destroys it. Driven by humiliation and rage, Ivy goes to Roux's apartment and loses her virginity to him. She regrets it immediately, destroys her diary, and resolves to reinvent herself, cutting Roux out of her life.
As punishment, her parents send Ivy to China for the summer. The night before, Meifeng tells Ivy the story of Nan's youth. Nan fell in love with a privileged boy named Anming Wu, but Meifeng separated them to shield Nan from the political persecutions of the Mao era, which targeted bourgeois families like the Wus. Anming died in a labor camp. Shen later proposed to the grief-stricken Nan, offering to sponsor Meifeng's other daughters for US immigration in exchange for Nan's hand. In China, Shen's wealthy cousin Sunrin Zhao lavishes Ivy with designer clothes and five-star hotels. When Ivy calls home, she learns the family has moved to Clarksville, New Jersey, without telling her.
High school in Clarksville is miserable. When Shen loses his job, the family plunges into financial hardship, and Ivy resumes shoplifting. They eventually recover when Nan begins reselling flea market items online. Ivy applies to a women's college near Boston, taking out loans over Nan's furious objections. Their final fight is brutal: Nan threatens suicide, and Ivy screams that Nan died with her old boyfriend in China. Ivy leaves at 18, determined to start over.
A decade later, Ivy is a 27-year-old first-grade teacher recently dumped by her boyfriend Daniel Sullivan. She encounters Gideon's older sister, Sylvia Speyer, at school pickup and is invited to a New Year's Eve party, where she reconnects with Gideon. Sylvia pushes Gideon to invite Ivy to brunch with his best friend, Tom Cross, and Tom's girlfriend, Marybeth Hamill. The foursome becomes regular, and after a ski trip, Gideon kisses Ivy.
Their courtship deepens, though Ivy finds Gideon rarely physically demonstrative. She enters his wealthy social world, meeting venture capitalist Dave Finley and his wife, Liana Finley, a Chinese-American former human rights lawyer. Inspired by Liana's example, Ivy decides to quit teaching and apply to law school. Gideon invites her to the Speyers' summer cottage, Finn Oaks, in Cattahasset.
At the cottage, Ivy is stunned to discover that Sylvia's boyfriend is Roux, now wealthy from businesses including laundromats and dollar stores, all linked to the Moretti crime network. Ivy fears Roux will reveal their history. Sylvia grows jealous of Roux's attention toward Ivy, and rain keeps everyone confined indoors. On a beach outing, Ivy tells Gideon she loves him. He says he cares about her "a lot," devastating her.
That night, Ivy goes to Roux's room, and they sleep together. He tells her he loves her, and she plans to leave Gideon. But the next morning, Gideon takes Ivy for a walk on the beach and proposes with his grandmother's sapphire ring, telling her he loves her. Ivy accepts instantly, abandoning Roux. When she tells Roux it was a mistake, he is furious and breaks up with Sylvia in front of the entire family before storming out.
During the engagement, Ivy senses a persistent distance in Gideon's affections. After Tom cruelly implies at dinner that Ivy is a gold digger, she calls Roux and begins a regular affair at his luxury apartment, stealing thousands of dollars from envelopes of cash he keeps in his drawers. Roux grows possessive, at one point slapping Ivy during an argument. He issues an ultimatum: She has two weeks to tell Gideon about the affair, or he will do it himself.
As the deadline approaches, Meifeng fractures her hip. At the hospital, Nan reveals a radically different version of her past: Anming sexually assaulted Nan and then pursued another girl. Terrified of social ruin, Nan wrote an anonymous letter exposing his family's corruption to a fanatical Communist official, leading to their arrest and Anming's death. Nan also engineered Shen's proposal by ensuring he overheard her desire to go to America. The secret to marriage, Nan tells Ivy, is giving a man something to fight for, even if the story is false.
This revelation transforms Ivy, who sees her own capacity for ruthlessness reflected in her mother. That night, Meifeng casually mentions she once stabbed and killed an intruder in China, expressing no regret. Ivy texts Roux, proposing a hiking trip on the day of his deadline.
Ivy drives Roux to the White Mountains, to a trail with a hidden ledge above a hundred-foot drop. She carries his phone and wallet. At a clearing, they share sandwiches and whiskey, and she tells Roux she has left Gideon. He believes her and speaks of their future together. At the ledge, she shouts a wish into the void, then urges Roux to take his turn. As he stands at the edge with his eyes closed, she pushes him off. She waits to confirm he is not moving, then hikes to the nearest town, disposes of all evidence, and catches a bus back to Boston.
Ivy collapses from scurvy caused by months of severe malnutrition. Months later, in spring, Roux's body is discovered by a hiker's dog. The death is ruled an accident. At Roux's small memorial, Ernesto Moretti, a Fox Hill acquaintance tied to Roux's criminal network, gives Ivy a hollowed-out book containing cash and a note: "Call me when you run out."
On her wedding day, Ivy slips outside and sees Gideon and Tom under a tree. As Tom departs, Gideon calls his name in an anguished stutter, his face contorted with pain. Ivy realizes with sudden clarity that Gideon is in love with Tom. She confronts Sylvia, who argues that Gideon needs hero worship and Ivy needs a hero. Ivy decides to proceed with the marriage. She reasons that they both have secrets, that mutual acceptance is enough, and that her real source of strength is her family. She walks to the altar, sees a look of peace on Gideon's face that mirrors her own, and does not look back.