The narrative unfolds on a bright summer morning, as Sang-woo (Seung-ho Yu) and his mother embark on a bus journey to the countryside. From the outset, it’s apparent that the unsophisticated demeanor of the rural passengers annoys the seven-year-old city boy. His mother is taking him to stay with his 78-year-old grandmother, Grandmother (Eul-boon Kim), who, despite being mute, is not deaf. This visit occurs while she seeks new employment after being abandoned by her husband and her failed business venture in Seoul. Their arrival is marked by a desolate bus stop in a quaint Korean village.
As Sang-woo arrives with junk food and toys, he shows no inclination to respect his mute grandmother, especially when discovering her home lacks basic amenities like electricity and running water. His mother apologizes for leaving him, assuring her own mother that the separation will be short-lived before she departs on the next bus. Left alone, Sang-woo dismisses his grandmother, refusing to even acknowledge her presence and derogatorily calling her a byungshin or "retard."
The following morning, the grandmother begins her daily routine by fetching clean water and washing clothes in the river while caring for her melons to sell at the farmer's market. Among her neighbors is a diligent country boy who makes attempts to befriend Sang-woo, who ultimately declines until a later reconciliation occurs. Additionally, there’s a young girl who captures Sang-woo’s affections, yet he soon discovers she is more intrigued by the country boy.
Living a humble and simple life, the grandmother shows deep care for her elderly friends. After some time spent playing, Sang-woo’s Game Boy runs out of batteries. In an act of selfishness, he seeks money for new batteries from his grandmother, only to find she has none. In his intolerance, he teases her and even resorts to throwing away her shoes, breaking her chamber pot, and defacing her home with graffiti.
Frustrated by her lack of funds, Sang-woo resorts to stealing his grandmother’s ornamental hairpin to trade for batteries. After a misguided attempt to barter at a shop, he finds himself receiving a painful smack on the head from a shop keeper—who turns out to be an acquaintance of his grandmother—and is sent home empty-handed.
One day, hungry for Kentucky Fried Chicken, Sang-woo expresses his wish in vague terms. Misunderstanding, the grandmother interprets his request as merely wanting "chicken." Determined, she goes to market under the pouring rain to buy a live chicken, only to return with a homemade boiled chicken instead of the desired fried one. Furious, Sang-woo tosses the meal aside but later succumbs to hunger and finishes it late that night. The next day, when his grandmother falls ill, he tenderly serves her the remaining chicken while taking care of her.
Despite the challenges faced by his grandmother, who suffers from osteoporosis, her reliance on Sang-woo is mostly limited to needing help threading sewing needles. She works diligently, stitching shoes and sharing her meager earnings with a friend who expresses a desire to see her again before it’s too late. Throughout this time, Sang-woo wrestles with feelings of anger and confusion in this unfamiliar setting, continually rebuffing her loving gestures.
However, the grandmother's unconditional love begins to break down Sang-woo’s defenses. One fateful day, he wakes early and accompanies her to the market, witnessing the relentless effort she puts into selling her vegetables. After a long day, she lovingly purchases noodles and shoes he had longed for. As they prepare to board the bus back home, Sang-woo modestly asks for a Choco Pie.
Visiting a shop owned by a dear friend of the grandmother who suffers from a bad knee, she is gifted several pies in exchange for a melon. Yet, upon her return to the bus, Sang-woo, eager to impress the girl he likes who is also aboard, decides he wants to ride alone. When she tries to insist he take the remaining produce, he stubbornly declines, and the bus departs. Alone, he waits impatiently for his grandmother to return, realizing only then that she had walked back carrying all of her wares.
Over time, Sang-woo gradually grows to love his grandmother. Acknowledging her illiteracy, he creates simple greeting cards to ensure she has something from him. Eventually, when his mother returns, Sang-woo prepares to go back to Seoul. His emotions pour out as the bus pulls away—he rushes to the back window, waving a tearful goodbye. The film concludes with the grandmother continuing her quiet life in their thatched-roof home, now enriched by the heartfelt letters from her grandson.
