The Turtles are lurking around their living room while Splinter prepares a trayful of sushi for himself. As he steps into the room, the Turtles spring out and engage each other in fights, which ultimately leads to Splinter slipping and destroying his entire lunch. Their newly irritable sensei orders them to expend their energy outside the lair somewhere.
At a mad scientist's laboratory, Dr. Polidorius has created a mutant fish named Ray, who possesses several abilities of different marine species. He's planning to create a new race of fish-people, and to sink the city by planting explosives in the sewers. Despite Ray's apathy, he reluctantly agrees to help after Polidorus pressures him.
April is covering the opening of a new Donald J. Lofty condo building when she spots a green face peeking out of the sewer, but much to her shock, it turns out to not be the Turtles. She follows the fish-man and ends up kidnapped by him. The Turtles follow, with no idea of the explosive charges that Ray is leaving behind.
Ray deposits April at Dr. Polidorius' lab, and Polidorius decides to turn her into another fish mutant who is to be Ray's mate.
As the Turtles search for April, they stumble across Ray, but he turns out to be a formidable opponent, with electric eel powers, scorpionfish spines, squid ink, a prehensile octopus tail, and considerable strength. They chase him down into the water, where they are unable to keep up.
Polidorius has to do some repairs to his mutation machine, which gives April a brief moment to try to contact the Turtles with a two-way radio. Donatello gets the signal on his Turtle Com, and they rush to get to Polidorius' lab. Unfortunately, Ray electrocutes them and Polidorius traps them in an energy cage, and they can only watch as April is mutated into a fish-person. When she emerges, she's green, webbed and covered in scales.
Raphael manages to release them from their cage, and Polidorius manages to escape from the lab. They discern that the explosives are going to be set off at noon, and race through the sewers to disarm as many of the bombs as they can. The only remaining bomb is under the Lofty condos, which sink under the ground as the entire street floods.
April now has sonar powers, which allows her to detect the location of Polidorius and Ray. She accidentally floods Polidorius' lab at the same time, and she and the Turtles rescue Lofty and Vernon from drowning. They drag Polidorius along, and force him to turn April back to normal.
Ray, meanwhile, has escaped into the sea, expressing his happiness at being free of Polidorius. When he asks some regular fish for directions, they flee,, afraid of him. But, he reflects, "it's home."
- Leonardo (Cam Clarke)
- Donatello (Barry Gordon)
- Michelangelo (Townsend Coleman)
- Raphael (Rob Paulsen)
- Splinter (Peter Renaday)
- April O'Neil (Renae Jacobs)
- Burne Thompson (Pat Fraley)
- Vernon Fenwick (Peter Renaday)
- Donald J. Lofty (Rob Paulsen)
- Dr. Polydorius (Alan Oppenheimer)
- Ray (Pat Fraley)
Home media releases
- Teenage Mutant Ninja Turtles: Rebel Without a Fin
- Teenage Mutant Ninja Turtles Season 4
- Teenage Mutant Ninja Turtles: The Complete Classic Series Collection
- Ray was initially supposed to be the character of Ray Fillet, but creator Ryan Brown, as well as Teenage Mutant Ninja Turtles Adventures writer Stephen Murphy, objected to this character being used as a villain. A fish mutant sharing the name of Ray was conceived in his stead.
- Ray pointing out his issues unethical implications of Polidorus's plans may have been added to the script to appease Ryan Brown.
- When Leonardo was finished talking to April on the Turtlecom the piece of footage of him, Donatello and Michaelangelo walking through the sewers from "Raphael Knocks 'em Dead" was played, this footage was also seen later in the episode when Leonardo said "Let's fan out and search for her!" when they were scouring the sewers for April just before another piece of footage of the water flowing on the sewer floor from the same episode was seen.