Krang and Shredders' scheming has The Turtles and New York afloat in confusion: Literately!
Shredder is using a new anti-gravity magnet to throw everyone in the city into the sky, and keep them there, with none, not even the TMNT, earthbound any more, Shredder and his hoods can do as they please, and using state-of-the-art anti-gravity boots to stay grounded. Krang informs Shredder of the instability of the magnet, and warns him not to overload it, but he is all but ignored by his partner.
The Turtles soon learn of Shredder's scheme, and, after managing to acquire a pair of gravity boots, are able to fend off the invading foot soldiers. Donatello notices that the birds are still flying, since they aren't bound by the laws of gravity, the magnet's power doesn't affect them, Donatello suggests to his bros that they head for the Turtle Blimp.
Angered by the Turtle's defiance, Shredder vows that if he can't own the city, he'll destroy it, by thrusting it completely off the planet!