A defrocked Tooth Fairy named Buster stumbles upon the Ghostbusters' television ad. Seeing a chance for friendship in a cold, cruel world, he moves in with them, certain he's their pal… but trouble soon follows.

Egon and Slimer switch minds and the timing couldn't be worse, as an egomaniacal ghost named the Master of Shadows (William Marshall) wishes to test his wits against the brainy 'buster', and destroy New York if he fails to measure up.