Carl discovers that Yin and Yang have forgotten Master Yo's birthday. Carl successfully tricks them into accepting a dangerous gift to give to Master Yo, so Yin and Yang won't be thought of as being thoughtless. But the gift is really a candle that once lit and blown out, switches the brains of Master Yo and Carl. Now Master Yo is in Carl's body, and Carl is in Master Yo's body. Carl plans to order the Woo Foo Warriors to their doom, while Master Yo finds out just what Carl has to deal with at his home.