It's the end of the world. A flood is coming. Luckily for Finny and his dad Dave, a couple of clumsy Nestrians, an Ark has been built and all animals are welcome… well almost all. Unfortunately for them, Nestrians are not on the list! But Dave has a plan, and Finny and he manage to sneak onto the Ark disguised as Grymps – much to the horror of real Grymps, Hazel and her daughter Leah.
However their troubles are just beginning as the two curious youngsters end up falling over board. Now Finny and Leah have to brave the elements in their quest to find higher ground while fighting off hungry predators and making unlikely friends. Meanwhile on board the Ark the parents must set aside their differences and hatch a plan to turn the boat around and make it back in time to rescue their kids.