Dave is a Nestrian, a colorful aardvark-like creature whose only real talents seem to be building cozy nests and releasing a foul-smelling blue gas when emotions rise. He drifts from place to place in search of a true home, a quest that wears on his son, Finny, who just wants to make friends and belong somewhere. As rumors spread of a flood that could cover the world, Dave gathers Finny and sets out with a caravan of other animals toward salvation: an ark large enough to hold every creature.
With a bit of ingenuity, some Nestrian craftsmanship, and the unexpected help of two Grymps—Hazel and her daughter Leah—the group manages to slip aboard the ark just as the threat seems over. But their bravado is short-lived: Dave and Hazel discover that [Finny] and [Leah] have vanished. Their curiosity got the better of them, and they had been on the scaffolding as a tidal wave struck, lifting the ship and carrying it away from the shore. The parents panic as the ark sails on, leaving their children stranded on the last bit of land not yet submerged, and a desperate race against time begins.
[Leah] and Finny, the younger pair of the voyage, face danger together. Leah, a born hunter, suddenly bears the burden of guiding a wary, awkward Finny, and together they manage to escape the rising waters, even as a pair of flying griffin-like predators circle in for a meal. Along the way, the children meet two more characters, Obesey and his companion Stayput, a squid-like parasite, who join the expanding group with their own quirks. With this new crew, Finny begins to reveal the brave hero inside him, steadying the ship’s smaller steps toward hope.
Back on deck, the parents must overcome their differences and work as a team to take control of the ark. They push through gorilla guards and confront the egotistical Lion Captain to steer the vessel toward safety. The “Fearless Four”—Dave, Hazel, Finny, and Leah—press on as threats intensify, including relentless griffins who target Leah and Finny. In a climactic turn, Obesey reveals himself to be connected to the sea in an unexpected way, and the threats around them start to fall as rising waters claim the attackers.
As the ark nears the mountain, Leah and Finny cling to the vessel with tenacity. After a perilous moment on an iceberg, Finny climbs aboard again but hesitates to leave Leah behind, leaping back to pull her up. Leah holds on with sharp claws as Finny makes a valiant effort to return, only to fall into the water. Dave attempts a rescue, and in a twist, the truth becomes clear: Nestrians are aquatic creatures, perfectly capable of breathing underwater. This revelation explains Dave’s long feeling of not belonging among the land-dwellers.
Griffins pursue the siblings, but Obesey, who is connected to the bowhead world, intervenes in a dramatic way, and the threat is eaten away as Dave and Finny swim alongside the ark, waving to Leah and Hazel. On the ark’s deck, the Lion Captain contemplates the fate of his passengers and whether telling Dave and Finny that they belong in the sea was the right or wrong choice.
In the end credits, the ark reaches Mount Ararat and the animals finally disembark. Dave and Finny discover that Nestrians belong to the sea, teaching Leah and Hazel to swim while the Griffins table a playful card game near a stack of fish inside Obesey’s stomach.
