Late at night, Leonardo drops in on Donatello as the latter is fine-tuning his inter-dimensional early warning system. When he finishes, he triggers a loud alarm that immediately wakes Michelangelo and Raphael, who decide to watch monster movies and read comics since they're already awake. Leonardo opts for ninja practice.
Unknown to them, Donatello's portable portal accidentally runs into the early warning system, switching on and opening a tear in the dimensional fabric. At the other side of the portal: a Dimension X prison, where two prisoners named Skaarg and Dementor have just attempted to escape. The guards gas them and tie them up, before locking them in solitary confinement. When the portal appears in front of them, they leap through. By coincidence, Irma and Vernon happen to be standing at the other end of the portal, and they are deposited in the jail cell.
In the lair, the Turtles are each pursuing his own interests when the early-warning system suddenly goes off. They rush to Donatello's lab, only to be told what happened with the dimensional portal. Concerned that Dimension X intruders may have crossed over, the Turtles head out to investigate.
Skaarg and Dementor soon discern that they are on Earth, and immediately start investigating the weapons and technology they can lay their hands on. They decide that they could use some help conquering the Earth from their old prison mates, the Dregma Brothers. As they consider how to get the Dregma Brothers to Earth, April finds them and attempts to videotape them, which the two convicts interpret as an attack.
April is chased away just as the Turtles arrive, and Donatello quickly confirms that the aliens are from Dimension X. Skaarg and Dementor prove to be formidable adversaries because of their superior strength and advanced weapons, but leave the scene when they hear that Donatello has a dimensional portal. They run into April once again, and melt her camera.
In Dimension X, Vernon attempts to throw his weight around with one of the guards, but quickly discovers that they aren't impressed. Also, they find that Dimension X food is revolting.
Skaarg and Dementor make their way to the lair, where they drive the Turtles back with laser beams and then trap them in a transparent forcefield. The two criminals use the inter-dimensional portal to bring the Dregma Brothers through from their cell in Dimension X. To make sure that they can't be sent back, they attach a time bomb to the portal and flee the lair.
Donatello manages to use a flashlight to short out the forcefield (though he isn't entirely sure how), and rushes to his lab to defuse the bomb. He's not sure which of the four wires to pull, and Raphael shouts at him that it's always the red wire... only for Donatello to pull the blue wire, declaring that it was all a trick. The other three Turtles head out to stop Skaarg and Dementor, while Donatello tries to find a way to send them back.
In Dimension X, Irma and Vernon are put on laundry duty, which is complicated by Vernon's whining and his overuse of detergent. Vernon also attracts negative attention from the guards during a prison yard run, but is terrified into continuing when the guard suddenly transforms into a more monstrous appearance.
Donatello advises his brothers that the aliens are probably going to the National Guard armory to get more weapons. He's correct, as the four aliens have gone there and begun reassembling parts of different vehicles and weapons; when the Turtles arrive, they're attacked by a flying tank bristling with laser cannons. As they attack the Dimension X convicts, Donatello informs Raphael that they have only one chance of sending the aliens back: they must be lured to the same place they appeared at, and conditions must be exactly the same. If it goes wrong, the whole city could be sucked into Dimension X.
The Turtles lure the felons to where they first appeared, and Donatello opens the portal... just as an old lady with a dog appears. As the dimensional balance begins to destabilize, Raphael manages to seize a levitating ray gun and send the old lady and dog elsewhere. The portal opens, pulling the convicts back into Dimension X and depositing Irma and Vernon on the street. Irma begins prattling about their experiences, much to the Turtles' bafflement.
In Dimension X, the four convicts are recaptured by the prison guards.
April reports on the events of the day, thanking the blushing Turtles for saving the Earth. Just then Michelangelo rushes in, declaring that there's been a huge tear in the fabric... but this time, it's of his undershorts, meaning they need a new washing machine.
- Leonardo (Cam Clarke)
- Donatello (Barry Gordon)
- Michaelangelo (Townsend Coleman)
- Raphael (Rob Paulsen)
- April O'Neil (Renae Jacobs)
- Vernon Fenwick (Peter Renaday)
- Irma Langinstein (Jennifer Darling)
- Burne Thompson (Pat Fraley)
- Skaarg (Pat Fraley)
- Dementor (Tony Jay)
- Hungry Dimension X Alien (Pat Fraley)
- First Dregma Brother (Townsend Coleman)
- Second Dremga Brother (Cam Clarke)
- First Dimension X Prison Guard (Barry Gordon)
- Second Dimension X Prison Guard (Peter Renaday)
- Third Dimension X Prison Guard (Barry Gordon)
- Exercise Prison Guard (Barry Gordon)
Home media releases
- Teenage Mutant Ninja Turtles: Convicts from Dimension X
- Teenage Mutant Ninja Turtles Season 7
- Teenage Mutant Ninja Turtles: The Complete Classic Series Collection
- When Leonardo asks what's wrong with the early warning system, he is seen with Raphael's colours.
- After April runs for the news van after the Turtles' fight with the convicts, Leonardo speaks in Raphael's voice.
- One of Raphel's sais gets melted during a fight in the lair, but he suddenly has it again moments later.
- When Leonardo, Michelangelo and Raphael are running away from Skarg and Dementor's Attack Vehicle, the three of them can be seen levitating in mid air as they run down the street.
- Why does Michelangelo have undershorts when he doesn't need to wear clothes?
- The dimensional balance is so fragile that conditions need to be identical to when the aliens arrived... yet the flying tank and the Turtles themselves don't seem to make a difference.