What's scarier that the Sassafras Siblings and Slovakian
Rot-Toothed Hopping Monkey Demons? The answer, my friends,
is OLD PEOPLE. And Billy is forced to face his fears when
his family picks up his great-aunt Tilley at Shady Acres to
bring her home for the long weekend.
Meanwhile, in Monstros City, a mysterious villain unleashes
a legendarily destructive monster: the enormous
Zis-Boom-Bah. Zis-Boom-Bah eats boulders for breakfast,
destroys cities with one step, and could make Monstros City
disappear faster than you can say, "Godzilla." He's got the
inhabitants of Monstros so riled up that the military wants
to use the OMG ("oh my gosh!") device, which will destroy
Zis-Boom-Bah but take half of Monstros with him. But Billy
has a revolutionary idea . . . which takes him a realization
about the scariest Old Person at Shady Acres.