Yin and Yang decide that they want their own headquarters, and Carl decides that he's tired of living with his mom. So Yin and Yang get a place in Master Yo's Outhouse while Carl tries to find an apartment to rent. Yin and Yang's problem is that the Outhouse isn't big enough, and Carl's problem is that three other villains are also laying claim to the place that Carl wants. Carl decides the four villains should share the apartment and become a League of Evil. Yin and Yang must find a way to defeat Carl, Smoke, Mr. Pondscum, and a new villain called the Puffin.