Sang Ly, her husband Ki Lim, and their infant son Nisay live in Stung Meanchey, the largest municipal waste dump in Phnom Penh, Cambodia. Like the other villagers in Stung Meanchey, they scratch out a meager living by picking through newly-arrived garbage and sorting out recyclable materials to sell to a scrap vendor. One day while Ki is out picking trash, a gang of youths beat him and steal his money, leaving him with a severe head wound that requires a trip to a local clinic. While he is gone, Sopeap Sin, Stung Meanchey’s old, drunken, and bitter Rent Collector, comes to Sang Ly’s one-room hut to demand their rent payment for the month. Sang Ly is unable to pay, and Sopeap threatens to evict them until she sees an illustrated children’s book sitting in their hut, which Ki had found in the dump earlier that day. Sopeap holds the book and reads through its pages silently, and since it obviously means a great deal to her, Sang Ly gives it to her as a gift. The old woman leaves silently with the book, and Ki returns with a bandaged head and a knife he has used the last of their money to buy, hoping to protect himself from the gangs. When Sopeap returns some time later, she forgives Sang Ly and Ki’s unpaid rent as thanks for the book. As she turns to leave, Sang Ly finds the nerve to ask Sopeap to teach her to read, to give her and her son hope in the midst of their poverty. Sopeap eventually agrees, but on the conditions that Sang Ly must study very hard and buy Sopeap good alcohol each week.
Sopeap misses their first lesson, discouraging Sang Ly, but while she is practicing a traditional healing remedy on her son—hoping to cure him of his unceasing diarrhea and illness—Sopeap arrives and apologizes, saying they will begin tomorrow. The Rent Collector’s sudden show of humility stuns Sang Ly. As Sopeap leaves, she reveals that not only can she read, which is rare in Stung Meanchey, she was once a literature professor at a university in Phnom Penh. Through Sopeap’s lessons, Sang Ly learns the Khmer alphabet quickly and soon is able to put the sounds together to read words, which thrills her, though Ki is less enthusiastic since he does not understand the point of reading or all the energy that Sang Ly invests in it. However, during one their lessons, Sopeap is half-drunk and vomits outside; there is blood mixed in with the bile, revealing that she is very ill.
After Sang Ly learns to read basic sentences, she begs Sopeap to teach her about literature as well, even though Sang Ly is not entirely sure what literature even is. Sopeap again resists, saying that literature requires both the mind and the heart, and she has spent all her drinking years trying avoid such emotional engagement. However, the old woman relents and tells Sang Ly that if she can find a piece of literature in the dump within just a few days, Sopeap will consider teaching her about literature. Sang Ly searches desperately but is unable to find anything that seems literary until the night before her next lesson, when her cousin tells her a poem orally passed down through her family for generations. When Sang Ly presents the poem to Sopeap, the former teacher reluctantly agrees to teach her about literature, though they will need to move through lessons quickly, because Sopeap plans to leave Stung Meanchey soon.
One day, while Sang Ly is cleaning her hut, a young orphan boy named Lucky Fat bursts in and begs Sang Ly to help him. A young girl named Maly is hiding in his hut. Since she is an orphan and her older brother is in a gang, Maly is at risk of being sold into child prostitution. Sang Ly, her mother Lena, and Ki spend the next several days helping Lucky Fat hide Maly from the gang members who are searching for her. When Sopeap discovers what is going on, she gives Sang Ly money to help Maly escape Stung Meanchey and be taken in by a good, protective family in Phnom Penh. Meanwhile, Sopeap continues to teach Sang Ly about literature, showing her that literature teaches about life, hope, and self-sacrificing heroism. In the midst of her teaching, Sopeap constantly hints that she is running from something in her past, drinking to forget who she once was. Even so, the teacher’s hard demeanor is slowly beginning to soften.
As time passes, Sang Ly tries more and more healing methods on Nisay, but nothing cures his illness and he grows weaker. However, Sang Ly dreams that Stung Meanchey is covered in snow, and in the distance she can see her home province, Prey Veng, as well as a man she once knew stretching his arms out towards her, welcoming her. When Sang Ly tells Sopeap about her dream during one of their lessons, Sopeap describes how important dreams are to literature and encourages her to ponder it, to figure out the dream’s true meaning.
In retribution for sheltering Maly, gang members beat up Lucky Fat and trash his hut. However, this encourages the villagers in Stung Meanchey to stand up to the gangs, even though they were formerly too fearful. Ki is excited, since he has been trying to enlist others to resist the gangs for weeks, but his enthusiasm wanes when the villagers beat one of the gang members to death. He and Sang Ly realize that the boy was only a teenager, Maly’s older brother. Sang Ly and Ki are both horrified, and Sang Ly reflects that just like in literature, good and evil and heroes and villains are hardly so simple as they first seem.
Sang Ly asks Sopeap if she can read the children’s book she gave her, and Sopeap agrees, gifting the book to Nisay. Sopeap reveals that the book was actually written by a close university friend of hers about Sopeap and her son. Later that evening, after Sopeap leaves, Sang Ly discovers that her teacher is dying of cancer, though she has been keeping it a secret. However, during their next literature lesson, as Sang Ly is angrily confronting Sopeap about her illness, Sang Ly’s mother arrives in a panic and tells Sang Ly that Nisay passed out and is now completely unresponsive. Terrified, Sang Ly rushes him to the nearby clinic, discovering that it is closed, before a benevolent taxi driver takes her to a modern children’s hospital. A nurse takes Nisay from Sang Ly, and after sitting all night in the waiting room, Sang Ly meets a doctor who tells her that Nisay will be alright, but he was severely dehydrated. When Sang Ly finally arrives home from the hospital, she falls asleep and dreams again of Stung Meanchey covered in snow and sees the man from her home province once again, recognizing him as the village’s local Healer. When she wakes, Sang Ly feels convinced that she must take Nisay to Prey Veng see the Healer, even though it is a long journey. Ki agrees to go with her. As they are about to leave Stung Meanchey, Sopeap arrives to say goodbye—looking very ill—and say that she wishes they could have finished their lessons. Sang Ly promises that they will resume their literature lessons when she returns, but Sopeap seems doubtful that she will survive that long.
Sang Ly, Ki, and Nisay travel by bus and by boat to Prey Veng, where they stay with Sang Ly’s extended family for several days. Sang Ly takes her son to meet the Healer, and he prepares a black tar-like substance that he injects into Nisay’s limbs. With the healing process performed, Ki and Sang Ly makes their way back to Stung Meanchey, arriving in the middle of the night, but they discover their hut was ransacked while they were away; they’ve lost everything. However, when Sang Ly awakes the next morning, she notices that Nisay seems healthy and active. Sang Ly decides that even if they have lost everything, they have truly gained everything if their child is finally healed. Over the next few days, neighbors rally together to replace what Sang Ly and Ki lost. Sang Ly hopes to see Sopeap but no one has seen the old woman for days and Sang Ly fears the worst. Lucky Fat arrives, however, with a notebook from Sopeap that is full of essays Sopeap wrote herself so that Sang Ly could continue to study, as well as a letter in which Sopeap says her final goodbyes, for she is going someplace to die and does not say where. A contact at the local hospital also reveals that Sopeap could have survived her cancer, had she sought treatment out of the country, but she willingly chose to stay and die so that she could finish Sang Ly’s education.
In the notebook, Sang Ly reads the last essay, in which Sopeap reveals the events of her life that brought her to Stung Meanchey. When Sopeap was a professor, her real name was Soriyan, and she lived in a wealthy area of Phnom Penh with her husband Samnang, her son, and a housekeeper named Sopeap Sin—the real Sopeap Sin. However, when the Khmer Rouge invaded the city in 1975, intent on killing all educated or intellectual people, Soriyan’s housekeeper pretended to be the professor and convinced the soldiers that the real Soriyan was a mere housekeeper named Sopeap Sin, thus sacrificing herself to let Soriyan live. The soldiers killed the real housekeeper, Soriyan’s husband, and her son, but they let the supposed housekeeper live. Soriyan kept the name Sopeap Sin and was haunted for the rest of her life by pain and guilt that someone else died in her place. When Sang Ly finishes the story, she is heartbroken but also convinced that Sopeap (her teacher) misinterpreted her own story, and she is desperate to find her teacher so she can show her her own value.
Sang Ly and Ki surmise that whoever owns Stung Meanchey might be able to help them find Sopeap, since she was their Rent Collector. When they go to the Ministry of Land and Records, however, they discover that Sopeap was not merely the Rent Collector, but also the owner of all Stung Meanchey, and that she has gifted her own home to Sang Ly and Ki and the rest of the property to the housekeeper’s surviving family. Sang Ly tracks down this family, the Sin family, and discovers that although they don’t know her teacher, the family has received anonymous packages of money every month for the last several decades, which funded their educations and lifted them out of poverty. Reading further through Sopeap’s notebook of essays, Sang Ly finally realizes that she must have gone to die in the house she once lived in. With the Sin family and Ki, Sang Ly finds Sopeap on her deathbed, graciously hosted by the new owner of the home she once lived in. Sang Ly introduces the Sin family, who have come to thank and honor Sopeap for her generosity, and Sang Ly sits with her as she dies.
When Sang Ly returns to Stung Meanchey, she tells the other villagers a fable about Sopeap, who seemed drunken and bitter but was secretly kind and generous, redeeming her memory.
