Air date: 12/28/87

New York City is on a crime wave; as reporter April O'Neil discovers, the thieves are ninja. As a street gang attacks April, she falls into the sewers, where four big talking turtles defeat the thugs, and take April to their lair. There April meets their mentor, the rat Splinter, who tells her his backstory as the Japanese ninja Hamato Yoshi. As the Turtles and April investigate the streets for the thieves' origins, they discover a group of robot ninjas, whose uniform Splinter recognizes as belonging to the Foot Clan.

Enter the Shredder

Air date: 12/29/87

Foot Clan leader Oroku Saki, the Shredder decides, along with his partner Krang from Dimension X to turn two thugs into mutant henchmen using the mutagen that created Splinter and the TMNT. Thus Bebop and Rocksteady are born using a stolen rhino and warthog from the zoo. The Foot Soldiers also kidnap Splinter, and the Turtles go rescue him at the Technodrome.

A Thing about Rats

Air date: 12/30/87

The Shredder hires the scientist Baxter Stockman, because his invention, rat-seeking robots named Mousers, can help him find Splinter. After an initial Mouser attack, the Turtles and Splinter go hide in April's apartment.

Hot-Rodding Teenagers from Dimension X

Air date: 12/31/87

Shredder opens the portal to Dimension X for the first time. Three teenage kids known as Neutrinos and two of Krang's stone warriors emerge. The turtles befriend the teens, but before long the two stone warriors set up a special weather making device that causes trouble.

Shredded and Splintered

Air date: 1/1/89

Shredder transmits a message to the turtles showing off a retromutagen gun that could turn Splinter back into a human. When Splinter goes after the gun Shredder then has completed Krang's new body and puts him in it. Then after the Turtles come to help Splinter they have to deal with Krang and his new body. Then after the turtles defeat Krang and Splinter destroys that retromutagen gun to save the turtles Shredder and Krang try to open the portal again. Fortunately Donatello reverses the polarity causing the entire Technodrome to be pulled into Dimension X.