The penguins battle with a giant fish terrorizing the ducks’ pond.
Eggy, Mother Duck, and her ducklings ask for the penguins’ help in getting rid of a monster in their pond. The penguins go fishing in the ducks' pond, as Skipper reminds his men that "Birds eat fish, not the other way around." Private then catches a small fish. Then suddenly, the monster fish the ducks described leaps out of the water and snatches at the hook, pulling all of the penguins into the water before shaking them off.
Everyone but Skipper are terrified at the monster fish they saw. Kowalski identifies it as the Snakehead Trout, a fish that devours everything in its path, leaving nothing but despair and tragedy in its wake. Refusing to walk away from this, Skipper has his team build a submarine. Unfortunately, once they assemble it, Private points out that it's too big to get out of their HQ. They then tear the sub apart and reassemble it in the park lake. Julien turns up to use a soda bottle to christen the submarine, but as the bottle is plastic, it fails to shatter. The penguins then take the sub underwater.
Skipper's team soon become paranoid to the point that they fire all weapons. When the submarine gets stuck in an old tire, Skipper goes outside to untangle it and is swallowed by the giant fish in the process (but not before mocking the other penguins).
The remaining penguins, under Kowalski's leadership, forge ahead to avenge Skipper. But since Kolwaski used up all their weapons earlier, they decide to collide their sub with the Snakehead. The penguins survive the collision and swim up to the surface. Unfortunately, the Snakehead had survived as well. Soon, the others see that Skipper is alive in the mouth of the fish and toss him a bottle of soda that had been shaken up earlier when Julien tried christening the submarine.
It causes the fish to blow up, and it is soon served as sushi by the penguins.