In a dystopian near-future Japan, a dog flu epidemic prompts the authoritarian Mayor Kobayashi to banish all dogs to Trash Island. Atari, a 12-year-old ward of the mayor, ventures to the island in search of his beloved pet, Spots. Upon arrival, Atari meets a pack of alpha dogs led by Chief, who despite his initial reluctance, becomes crucial to Atari's quest. The group navigates the island's treacherous terrain, encountering stray packs, deadly traps, and hostile environments. Throughout their journey, they form a special bond, overcoming differences to work together toward a common goal.

While Atari and his newfound friends struggle for survival on Trash Island, a determined young foreign exchange student named Tracy begins her own investigation into the canine quarantine back in Megasaki City. Through her discoveries, Tracy exposes a vast conspiracy that threatens not only the dogs but also the human population. As the narrative unfolds, touching on themes of loyalty, sacrifice, and resilience, the story races towards a climax that will determine the fate of both the exiled dogs and the society from which they were cast out.