Like all the rats in his tribe, Vasco loves nothing more than to scurry around the harbor in search of discarded fish. But one day he discovers that the members of his tribe have died under mysterious circumstances. Now Vasco is alone until he reluctantly joins some fearsome rats who live deep in the sewers. Among them, he makes some loyal friends and some daunting enemies. And, as he begins to understand that humans are masterminding the extinction of all the rats in the city, Vasco sees only one solution: to flee aboard a ship. Courageous, humble, and determined, Vasco does his best to guide his exiled companions to a faraway land where they can live peacefully. But in struggling to establish a new tribe, and to find a place they can call home, Vasco must endure countless dangers and rise to many challenges.