The world is on the brink of destruction as a massive flood approaches. Fortunately, Dave and his son Finny, a pair of awkward Nestrians, discover that an Ark has been constructed to rescue all the animals. However, they soon learn that Nestrians are not permitted on board. With the reluctant assistance of Hazel and her daughter Leah, two Grymps, they manage to sneak onto the Ark, believing they are safe. But their relief is short-lived when the adventurous youngsters accidentally tumble off the vessel. Now, Finny and Leah must navigate the rising waters and evade dangerous predators as they strive to reach a mountain peak, while Dave and Hazel must overcome their differences, turn the Ark around, and rescue their children. The journey promises to be anything but easy.