Four aliens - Gleep, Romtu, Scoota, and Bing - have been sent to Earth from the planet Mars in order to find a rare material known as "coobi" (which is later revealed to be candy). After crash landing on Earth, they wander the streets searching for "coobi," but are mistaken for trick-or-treaters and ignored. When Scoota gets a strong reading on his "coobi meter," the four aliens chase down two children, Jeanie and Michael, into the woods. The children learn about the aliens' mission and agree to help them collect candy.
Meanwhile, Mrs. Gizbourne and her assistant Hans are in an old house performing experiments on insects to find the secrets of eternal youth. It is revealed that by performing these experiments they have nearly drained Crystal Lake, which is the main source of power for a candy factory in town. Mrs. Gizbourne then demands that Hans find a bug "big and strong enough to survive a nuclear meltdown."
The special returns to the children and the aliens. They agree to split into two groups to find more candy, one group consisting of Gleep, Romtu, and Scoota and the other group consisting of Jeanie, Michael and Bing. The children become distraught when they learn that Bing is running towards Mrs. Gizbourne's house. Hans mistakes Bing for a giant insect and proceeds to capture Bing and bring him to Mrs. Gizbourne. The children learn of Mrs. Gizbourne's plot, but are soon captured by Hans. Jeanie and Michael are quickly able to escape with Bing in tow to the lake. There they are found by Jeanie and Michael's father, who goes on to thwart Mrs. Gizbourne's plans. The first group of aliens then arrive at the candy factory, take all of the candy, give Michael a special skipping stone and return to Mars. Michael uses this stone and the power of wishing to revive Crystal Lake. The candy factory is thus saved, and the townspeople end the special rejoicing.
|Rhea Perlman||Mrs. Gizborne|
|William Hanna||Narrator (voice)|
|Will Estes||Michael (as Will Nipper)|
|Michael D. Roberts||Accountant|
|Don Messick||Romtu (voice)|
|Paul Williams||Gleep (voice)|
|Tim Anderson||Fred Flinstone|