Coop's mom is throwing a "welcome back/thanks for saving the world all by yourself" party, and Yin and Yang are the only ones not invited. Meanwhile, three flunkies join together and try to get into The Night Master's fortress. However, they need the spare key, which the Night Master gave to Coop!

Yang's brain becomes controlled by a villain known as Mastermind.

Yin and Yang search for their parents after Yin is drained of her aura and only a transfusion from a parent will save her.