The Shredder kidnaps Splinter in an attempt to lure the Turtles to his own cause. In order to rescue Splinter the Turtles must enter the Shredder's mobile fortress and brave it's dangerous weaponry.

Baxter Stockman, a mad scientist, is showing an exterminator his new invention: a rat catching robot called Mousers.

Shredder experiments with the Inter-Dimensional Portal, hoping to contact Krangs' Rock Soldiers and prepare an invasion of Earth, but a group of fun-loving aliens called the Neutrionos, renegades in Krang's dimension, take advantage of the Portal's opening and use it to arrive on Earth.

As Shredder lures Splinter into he Technodrome, this time with the promise that a weapon in his possession can restore the sensei to human form, the Turtles confront a giant-sized Krang, now in a new body, in the heart of New York City.