Jin is an intelligent young girl who shares her life with her mother and younger sister, Bin. While she excels in her studies, she often finds herself distracted from household responsibilities and has occasional bedwetting incidents. One day, upon returning home, Jin discovers that people are emptying their family apartment of furniture. This unsettling experience prompts their mother to take Jin and Bin to stay with Big Aunt, their paternal aunt who lives outside the hustle and bustle of the city. Before parting ways, their mother leaves them a piggy bank, assuring them that Big Aunt will reward them with change for their good behavior; once the bank is full, she promises to return.
Grief-stricken by her mother’s absence, Jin finds herself crying often and refusing to eat, while Bin appears to cope better with their circumstances. As they adapt, Bin forms a friendship with a neighborhood boy who has Down syndrome. His caring mother treats them kindly and starts to take notice of the struggles the girls are facing. However, it becomes evident that Big Aunt is battling her own demons as an alcoholic who frequently passes out or is too hung over to fulfill the duties of caring for the children, forcing them to fend for themselves. Inspired by another local boy who gifts Bin some roasted grasshoppers, the sisters get the idea to cook and sell them to fill their piggy bank. This venture proves fruitful at first, but as summer fades, so do the grasshopper supplies. In a clever twist, Bin devises a plan to make change from their higher-value coins, quickly boosting their savings.
The girls attempt to reach out to their mother via a young man’s cell phone, only to discover that the number is disconnected. Yet, the sisters remain hopeful, waiting at the bus stop where they last laid eyes on their mother, despite her never returning. Eventually, Big Aunt discloses that she received a letter from their mother. In it, their mother confesses that luck hasn’t been on her side with their father and admits her inability to provide for the children. Instead, she suggests that Big Aunt take them to stay with their maternal grandparents on a farm.
Arriving at their new home, the girls soon face their grandfather's displeasure at having them brought there as an added burden. Meanwhile, their grandmother greets them with warmth and kindness, ushering them into their grandparents' modest but lively life. When the girls ask for winter shoes, it becomes clear that their grandmother's own footwear is in tatters. Motivated by love and kindness, they decide to offer her their piggy bank so she can buy new shoes. Although both Jin and Bin lost trust in their mother due to her absence, they make a solemn promise to one another—pinky swearing that their mother will eventually return for them.
