Leafie [Moon So-ri] lives on a crowded battery cage chicken farm with many other egg-laying hens. She dreams of becoming a mother, but she cannot incubate eggs. In a bold, desperation-fueled plan, she fakes a faint, hoping the farmer will remove her with the others believed dead. When the farmer leaves, Leafie slowly wakes, only to be confronted by a one-eyed weasel named One-Eye [Kim Sang-hyun]. Her life is saved by Wanderer [Choi Min-sik], a wandering mallard, who traps the weasel in the farmer’s wheelbarrow and then departs without sharing his name.
Thrown back into a crowded yard, Leafie finds the other animals wary of her, and the barnyard rooster [Um Sang-hyun] refuses to let her join his flock, insisting that her place is to spend her days laying eggs. With nowhere else to go, she heads into the wild, where a new chapter begins. In the wild, she meets Mr. Otter (a fellow creature without a listed actor in this cast) who has heard of Leafie and helps her find a place to live on Wanderer’s behalf. Leafie crosses paths with Wanderer again and discovers he has a mate, Wanderer’s Mate / Yard Hen [Kim Ji-hye], though that very night One-Eye attacks and Wanderer’s mate is tragically killed.
Before Wanderer dies, he entrusts Leafie with one purpose: to guard his egg for a few days and, more importantly, to take his unborn child to the Everglades. He leaves Leafie to exact revenge on One-Eye and to protect the impending life. That same night, One-Eye returns, and Wanderer engages her in a fight to the death. Wanderer is killed, and Leafie is left heartbroken, gripping the nest and the fragile future it holds.
From there, the egg hatches into a duckling that imprints on Leafie, believing the hen is its mother. Leafie tearfully accepts the responsibility and names him Greenie [Yoo Seung-ho], a choice that marks the start of a long, intimate bond between them as they head toward the glade Wanderer once spoke of.
Leafie raises Greenie with quiet determination, and Mr. Otter teaches him to swim. To help, they call in a Bat [Hong Bum-ki] and an Owl [Seo Seung-won], who assist the growing duck in learning to fly. As Greenie matures, he tries to befriend Mandarin ducks, but they mock Leafie and question the pair’s place in the waterfowl community. The news from the water birds is harsh: Leafie’s presence is seen as an oddity, and Greenie shoulders the blame alongside her. This leaves Greenie feeling isolated, and he begins to blame Leafie for the lack of acceptance he experiences.
Chirpie, a sparrow friend of Leafie, warns them that the farmer plans to clip Greenie’s wings. To distract the farmer, Leafie and Mr. Otter release all the hens from their cages, triggering a dramatic escape. Leafie reunites with Greenie, while Mr. Otter bites through the tether that holds him down, enabling a broader escape. The farmer’s Rooster stops them, and the truth about the Rooster’s fake comb is revealed as one of the ducks steps forward to take charge. Leafie, Greenie, and Mr. Otter make a risky exit from the farm, and the trio parts ways as they continue their journey.
On their way, One-Eye again pursues Greenie, and the two birds are forced into a harrowing confrontation. Leafie intervenes, but One-Eye pins Greenie to an old tree. The branch breaks, sending Leafie and Greenie tumbling toward a cliff. Leafie mourns what she believes to be Greenie’s death, but Greenie survives the fall and, through perseverance, learns to fly. One-Eye clings to a ledge, herself surviving the moment.
Autumn arrives, and a flock of ducks returns to the Everglades. Leafie finally understands Wanderer’s instruction: her mission was to guide Greenie to a world where he can grow and belong. An adult Greenie meets his flock and learns of an upcoming contest to decide who will be the new guard duck. A rivalry soon forms between Greenie and Red Head [Sa Seong-ung], while Leafie quietly supports him, helping remove a fragment of human string from Greenie’s leg just in time.
Greenie enters the contest, driven by the mentor’s memory and his own evolving sense of belonging. He triumphs, winning a position as the flock’s guard duck. After the victory, Leafie discovers a nest of baby weasels and begins to care for them, a surprising responsibility that deepens her bond with the world around her. Rooster finds a new home with Mr. Otter after escaping the farm, and Greenie tries to say goodbye to Leafie before joining his flock once more. But danger remains: One-Eye returns, and in a confrontation, Leafie steps in to protect Greenie. One-Eye threatens Leafie to stay away, and the two birds find themselves at the nest of the baby weasels. To Leafie’s horror, the baby weasels turn out to be One-Eye’s offspring, a grim realization that One-Eye was simply killing to feed her own young.
With that revelation, Leafie understands the cycle of survival that governs One-Eye’s world. She and Greenie escape the scene, and the autumn journey carries them toward a new life for Greenie. The flock of ducks prepares to leave the Everglades, and Leafie and Greenie share a heartfelt farewell before Greenie departs with his flock. Leafie, now realising she never learned to fly, contemplates her own place in the world. In a climactic choice, she decides to sacrifice herself so One-Eye can feed her offspring, allowing Greenie to continue his life with the flock. One-Eye kills Leafie, and the ending lingers on the implication that One-Eye may fly in spirit, watching as Greenie soars with his new family.
