Inspector Gadget is assigned to look into a case of some missing oceanographers who were searching for an undersea city when they disappeared.

In the far-off country of Pianostan, the people remain happy as long as their King is miserable. But M.A.D. has been ensuring that the King is happy in order to disrupt the peace, so Inspector Gadget is sent out to investigate. To further complicate matters, the King looks exactly like the Inspector!