Using a hypnotic microphone and speaker, Shredder takes over a radio station and broadcasts a signal that sends the population of New York City sailing into a dimensional limbo dubbed "Krang's Chasm".

A mad professor named Mindbender creates a law-enforcement robot named "LEX" to clean up crime in New York, but LEX ultimately starts arresting numerous innocent people for the smallest infraction. With the other Turtles unreachable, Leonardo must discover his own innate skills to stop this rogue robot before he and Mindbender declare themselves dictators of the city.