The narrative flashes back to July 2004 in a village called Lakeyard, where Song gives birth to River in her family’s home. Her husband, Blue, suggests the name River because it symbolizes endlessness. During the traditional month of postpartum confinement, Song is cared for by her mother, who is a stern and practical woman. The family is poor, and Song’s older brother is unemployed and drinks heavily. Blue, a kind and supportive husband, cares for Song and carves two clothespin dolls, one resembling himself and one resembling Song, for their new family.

To earn money, Song begins making earrings at night. It becomes clear that both she and Blue will have to leave the village as migrant workers to support their families. Blue recalls how they met two years prior when he, a quiet construction worker, defended her from officials who were confiscating her pineapple cart. They fell in love, married, and briefly ran a successful hotcake business before circumstances forced them to return to the village for River’s birth. At the end of the month, Blue leaves for Shenyang to find work, promising they will reunite for the Spring Festival. He gives River the two clothespin dolls before he departs, leaving Song and their son behind.

The narrative returns to River’s perspective immediately after he is separated from his mother in the Beijing Railway Station. After retrieving his music book, he panics when he cannot find Song in the crowd. He is nearly trampled before crawling to safety in an alcove between escalators. Realizing he needs a phone to call her, he is approached by a suspicious, veiny-eyed man who offers to help. The man claims his phone is in his car and tries to lead River out of the station.

River senses danger and runs away, but the man pursues him relentlessly through the crowd. Remembering a game of hide-and-seek he played as a child, River uses the crowd as cover, hiding behind people to evade the man. He escapes the station into the cold public square outside. Still being followed, he hides behind a sweet potato vendor’s cart. The man finds him there and tries to convince the vendor that River is his lost son. River seizes the opportunity to bolt, leaving his asthma medicine behind in his haste. He runs across a footbridge and into the city streets, eventually realizing he is far from the station, completely lost in Beijing.

In November 2004, four months after River’s birth, Song’s mother tells her it is time to leave for Harbin to find work. Distraught at the thought of leaving her baby, Song decides to ask her mother for permission to stay longer, or even to accompany her to Harbin to help care for River. The next day, Song begs her mother for help, but her mother laughs at the idea, stating they need money, not sentiment. When Song refuses to leave River, her mother slaps her and calls her a failure.

Devastated but resolute, Song decides to take River with her. As River cries, a classical music piece on the radio, Debussy’s Arabesque No. 1, calms him, inspiring Song. She packs their belongings, creates a makeshift cradle from a drawer, and secures it to her scooter. Ignoring her mother’s prediction that she will “come crawling home in shame” (46), Song drives away from Lakeyard with River. She arrives in Harbin and rents a small, bare room, using the last of her money. Determined to make a life for them, she sets up their new home, playing the radio for River as they begin their adventure together.

Trapped in the crowd, Song is forced out of the east exit of the station. She realizes River’s instinct would be to hide, and she hopes he will find a phone to call her. As she waits, she notices her phone’s battery is low. Her phone is then stolen by two men. When she accuses them, a nearby police officer dismisses her and sides with the thieves. As they walk away, she attacks one of them, but the officer grabs her and drags her out of the station, threatening her with jail if she returns.

Now phoneless and barred from re-entering the station, Song begins a frantic search of the square. She speaks to a sweet potato vendor, who confirms seeing a boy in a yellow jacket. The vendor tells Song that a suspicious man was looking for River, but River ran away from him, escaping over the pedestrian footbridge. The news that River is lost in the vast city is destructive to Song. As Song prepares to cross the footbridge to continue her search, she finds the blue tube of River’s asthma inhaler on the ground.

The story flashes back to January 2007. Song and two-and-a-half-year-old River live in a small room in Harbin. Song works long hours as a cleaner for an agency run by a woman named Mrs. Zhang, carrying River on her back from job to job. The city’s severe winter air pollution has caused River to develop a chronic cough. After two years of separation, Song and Blue are finally planning to reunite for the New Year holiday.

One morning, Song receives a call from Blue’s company informing her that he died in an on-site accident, having fallen from a scaffold during a storm. Numb, Song goes to her first cleaning appointment and calls her mother, who is unsympathetic and practical, advising her to sue the company. Song rejects her mother’s offer to come home, stating she no longer needs her help. That night, River’s coughing worsens, and he experiences a severe asthma attack. Song rushes him to a community clinic, where a doctor diagnoses him with asthma, linking it to the chronic air pollution. The doctor explains it is a lifelong condition with no cure and that the air quality poses long-term health risks. Holding her son, Song vows to find a way to protect him.

After getting lost, River finds his way back into the train station with the help of Guo Bing, a kind, middle-aged night janitor. River explains that he is waiting for his mother, and Bing allows him to stay in the large, mostly empty second-floor Waiting Area. He shares his tea eggs with River and tries to call Song, but her phone is still off. As the station closes for the night, Bing offers River his small, windowless room (revealed to be a converted supply closet) to sleep in. He warns River to avoid his impatient and unfriendly supervisor.

River settles into the bed but feels anxious, fearing that something bad has happened to his mother, just as it had to his father. He is grateful for Bing’s kindness and feels a sense of safety in the train station. In Bing’s room, surrounded by the hum of the station, River hears the Tchaikovsky concerto in his head. He believes that the music is a connection to his mother and that she will follow the sound back to him, no matter how long it takes.

In a flashback to August 2008, four-year-old River discovers a piano at one of Song’s cleaning jobs. He is instantly fascinated and, to Song’s astonishment, figures out how to play “Twinkle, Twinkle, Little Star” by ear after hearing her sing it. This revelation convinces Song that River is a prodigy and that the piano is his path to escaping a life of poverty and hardship.

She finds a highly regarded teacher, Professor Li, who immediately recognizes River’s rare talent, calling him a “little wonder.” Professor Li agrees to teach River for free, and lessons begin. River shows perfect pitch and rapidly develops his skills under Professor Li’s demanding Russian technique. Using the compensation money from Blue’s death, Song buys River an upright piano for their small room. River practices diligently, and Song supports him, learning musical terms to help him. The piano becomes the center of their lives and Song’s plan for River’s future.

On her first night lost in Beijing, Song finds shelter in a small, empty church. A pastor finds her there and offers comfort, telling her about God’s son, who also rose after being lost. This message gives Song renewed faith that River will survive and ultimately succeed. The next morning, she goes to a bank to withdraw her savings. While rushing, she nearly collides with a food delivery worker who crashes his scooter to avoid hitting her. The worker, a cheerful man who calls himself White Dragon, is uninjured and helps her find a bank and a cheap motel.

Song buys a new phone but is unable to recover her old number, severing her last digital link to River. After the train station’s Lost and Found confirms they have not found River, she files a report with the police, who are unhelpful. A week into her search, Song realizes she can make money while looking for River by becoming a delivery worker herself. She runs into White Dragon again, who helps her sign up for the delivery app and offers her a room for rent in a courtyard house with other workers. Her application is approved, and she prepares to start her new job and continue her investigation.

In October 2012, eight-year-old River prepares for his first piano competition. His severe stage fright causes him to flee the stage before he can play. To help him overcome his anxiety, Song gives him the “girl” clothespin doll to carry with him as a talisman. At the next competition, he manages to get through his performance. Over the next two years, he and Song travel constantly for competitions, but his stage fright remains a persistent obstacle, leading to inconsistent results. Professor Li, who is heavily invested in River’s success, becomes increasingly frustrated.

The day before a major competition in Harbin, River meets another young pianist, a confident girl from Beijing who calls herself “the Bachist,” whose real name is Mini. She is a student of the renowned Professor Tiger. At the competition, River’s stage fright returns. Professor Li, desperate for River to win, gives him beta-blockers without Song’s knowledge. Onstage, the medication interacts with River’s asthma and triggers a severe attack, causing him to collapse.

For weeks, River lives secretly in the train station, using Bing’s orange janitor coat as a disguise to move around undetected while he waits for his mother. When he can no longer reach Song’s phone number, he fears she may not return. One night, while unable to sleep, he discovers an old, broken-down piano in a locked storage closet under a staircase. He begins practicing secretly at night, which restores his spirits and sense of purpose.

He is discovered by Phyllis, an elegant older woman and former concert pianist who takes the first train to Tianjin every morning. Intrigued by his playing, she begins bringing him breakfast. After several days, she reveals her past and critiques River’s technique, which she identifies as that of a “showman.” She offers to take him with her and teach him properly. Torn between waiting for his mother and seizing this opportunity, River ultimately decides to go with Phyllis, believing it is what his mother would want. He leaves the station without waking Bing, but Bing calls out, telling River he can always come back to visit.

The narrative returns to the day of the major Harbin competition in November 2015. At the conservatory, Song and an anxious 11-year-old River see the immense scale of the competition and the wealth of the other families. In line, they again meet Mini the Bachist, whose teacher, Professor Tiger, is a judge. 

After River’s on-stage collapse, a doctor explains that the beta-blockers given to him by Professor Li caused the asthma attack and could have killed him. Professor Li confesses he gave River the pill out of a desperate need for him to succeed.

Furious and feeling betrayed, Song fires Professor Li. She realizes his mentorship was driven by his own ambition to share in River’s glory. Afterward, Song sits with River in the empty auditorium and formulates a new plan. She decides they will move to Beijing before the New Year. There, she will find a way for River to play for Professor Tiger, whom she believes is the best teacher in the country and the key to River’s future. This decision leads them to be on the train to Beijing at the start of the novel.