The special begins at Cylindria's, where the UltraToons are discussing Nightmare Night, a Halloween-type holiday that replaces Halloween in UltraToon City because, when Halloween was invented, the mayor of the city at the time, Vicky the Evil Overlord (ancestor of Vicky) banned Halloween because she hated it from experience. The Mayor announces that costumes can be made or bought for the night.
As the days before Nightmare Night progress, Gretchen prepares a "Gret Chick" costume to reflect her "idea of being a werechicken after such a loooooong time of being human".
As Nightmare Night begins, the gang get in their costumes while Gret, in the finished "Gret Chick" costume, gets the people together and they do "candy stealing", which is the Nightmare Night version of trick-or-treating.
Suddenly, Buttercup lets a ghost case with live ghosts inside open, resulting in UltraToon City being attacked by ghosts!
The gang calls on the powers of the city's heroes to stop the ghosts. Suddenly, a strange figure appears, a strange man calling himself "The Toon Master" (a caricature of Émile Cohl), who uses his hypnotic powers to stop the ghosts and make the night safe.
At the end of the special, the trick-or-treators put their costumes into the cupboard except for Gret, who puts the custome into her clothing section, but then the costume's eyes glow red.