The end of the world is near: the Great Deluge arrives. Fortunately, Noah built an Ark to accommodate all the animals. All except Dave and his son Finny, who belong to the race of the Nestrians-curious and adorable creatures whom nobody thought it useful to invite on board the Ark. Thanks to the involuntary help of two fierce Grymps, Hazel and his daughter Leah, the Nestrians manage to embark discreetly. But at the moment of departure, Finny and Leah accidentally fall from the boat. They will then have to unite to escape the Flood and survive in a hostile world populated by wild predators.