The penguins battle with a giant fish terrorizing the ducks’ pond.
The penguins were about to start their swimming exercise but were interrupted by Eggy, Mother Duck, and her ducklings swimming around in their water. The penguins try to chase them off, only for the ducks to beg for the penguins’ help in getting rid of a monster in their pond. At first, the penguins didn't take the ducks seriously and 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. They laughed it off and were about to quit the expedition when 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 a Snakehead Trout, an invasive species of fish that devours everything in its path, leaving nothing but despair and tragedy in its wake. Refusing to walk away from this and let the duck's pond get destroyed by the invasive fish, Skipper has his team build a submarine to kill it by fighting the predator at its own game. 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 just as Julien gives them the bottle.
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 and scolding the other penguins for their cowardice).
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.