When they were kids, Tom takes Jerry fishing and Jerry's the bait. As Jerry tries to escape danger while underwater, he was running out of air. Until he was saved by a mermouse and becomes quite enamored with her as she gives him a form of a mermouse with gills. She takes him to her home called Atlants. But when Tom, in a subminre, sees the mermouse himself, Jerry must save Atlants and his new friend from being exploted by Tom.