Jerry meets a Beautiful Mermouse and tries to protect Her from Tom, who would exploit Her.
We see Tom talking a stroll down by the pier with his fishing gear. When he reaches the end of the pier he set up to fish with Jerry as his lure. As Jerry descends in the water, a barracuda takes notice of Jerry. As Jerry is fighting off the barracuda, a green, female Mermouse sees the chase and rushes to save Jerry. After the rescue, Jerry can't believe his eyes that he was rescued by a Mermouse. The Mermouse seems rather smitten with Jerry. but as He approaches the Mermouse, Jerry is pulled up by Tom. The Mermouse unties Jerry and then takes the fishing line and ties it to a buried chest. Tom pulls up the chest and it flies up out of the water, into the air, and then crashes down on Tom through the pier taking Tom down into the depths below. As Jerry and the Mermouse play catch with a giant pearl,
Tom recovers and sees the Mermouse. Tom instantly becomes overwhelmed by Greed and plots to capture the Mermouse, but Jerry is there to rescue her with the help of a lobster. The two mice swim away with Tom close behind, but they lose Tom in an underwater cave where he crashes into an angry Octopus. The Octopus beats Tom and throws him towards a boulder where Jerry and the Mermouse were hiding. Tom then chases after the two mice again as they lead Tom toward a sunken ship. As they chase back and forth, Tom puts Jerry in a chest and locks him up and then chases after the Mermouse. They both swim back and forth crossing paths with a swordfish in the process and as Tom traps the Mermouse in a diving Helmet, the swordfish to chases after Tom and spear him out of the ocean as Jerry frees the Mermouse. as Jerry and the Mermouse are now taking a relaxing ride on a sea turtle, the Mermouse Kisses Jerry, making Him become Lovestruck, until Tom drops a net and captures the Mermouse and speeds away on a boat. Jerry, still on the turtle, begins a speedy chase on the now wound up turtle. We see Tom rush into the Ocean View Aquarium and leave with a big wad of money.
That night, the Mermouse is inside a Display Tank sorrowing, but sees Jerry with a grappling hook and helps Her escape. As Tom is at home counting his money and watching TV, a news bulletin breaks of the Aquarium offering a $100,000 reward for the missing Mermouse's Return. Tom heads back to the pier just as Jerry and the Mermouse arrive. Jerry throws the Mermouse back in the ocean, but not before the Mermouse Kisses Jerry. Tom is waiting to give chase. The Mermouse manages to escape Tom, but he is close behind as the Mermouse heads up to a sleeping Water God who awakes and sends Tom running away by shooting lightning at him. The Water God then lifts Jerry and the Mermouse out onto a rock by the shore and the two mice stare off into the moonlight. then, we iris out.
- Despite being air breathers, Tom and Jerry went for minutes without needing air, from being underwater for so long.
- When we see the Mermouse shedding tears in the Aquarium's tank, her muzzle is white, not beige.