Yo tells Yin to go to the valley of the two-ni-corns and find a rainbow mane The Gnu to fix her toy. Meanwhile, Yang is taken over by Ultimoose.

Yin meets a hamster who loves to clean while she is out buying cleaning supplies. The hamster reveals himself to be Fastidious, and asks the Woo Foo students to help him defeat some of the spirits who have been making a mess. However, there is something sinister about Fastidious.