Dib is doing experiments with his father's equipment until it goes
wrong. Dib manages to launch a potal into a monster world in his
forehead. Dib now starts passing in and out of an alternate dimension
where everything is evil. He manages to force Zim to come into the
dimension with him. The monsters capture Zim and say they won't release
him if Dib doesn't "surrender his head." It is revealed that Dib's head
is the only portal out of the dimension, and all the evil creatures
within it want to go through it. Zim saves Dib so that he can get
through the portal but he then leaves Dib to the monsters. The monsters
have a look through the portal but turn back as they are disgusted by
the sight of GIR eating candy.