A Zen Master disciple, Yen Lo, is mortally wounded by the Zen Master's daughter, An Ling, when he tries to kill her father. Yen Lo vows he will be back to kill both the Zen Master and An Ling. He enters Limbo, where his wound will not progress, and his physical body will remain alive.
At the manor, Phoebe is training in martial arts with Cole to prepare to fight the Source. Meanwhile, Piper is teaching Paige about potions and preparing her for a quiz. However, Paige feels that going out and fighting demons is more important than sitting and studying. Piper warns her that one mistake can hurt someone, then leaves to get more ingredients at a Chinese herb store. Standing over a boiling pot, Paige adds ingredients at random, then wishes she were able to fight like Phoebe. The potion causes Paige and Phoebe to switch bodies. Not wanting to make Piper any madder at her, Paige convinces Phoebe to not tell anyone what has happened, and the two pretend everything is normal.
At the herb store, Piper meets An Ling, who is trying to get the dragon blade, which will remove Yen Lo's soul from his body so he can move on. Piper agrees to help An Ling fight this evil.
Yen Lo appears at the manor, traveling out of Limbo through the clouds, since water serves as a portal. Paige, in Phoebe's body, cannot levitate properly to kick him. Yen Lo gets the dragon blade as a result and escapes. Piper finds out about the botched potion. The sisters make a new potion and reverse the spell, putting everyone back to normal.
Piper agrees to switch souls with the Zen Master, whom Yen Lo has stabbed and taken with him to Limbo. The Zen Master, in Piper's body, is able to take An Ling, Phoebe and Paige to Limbo, and Paige learns how to use her powers just in time to get the dragon blade from Yen Lo. Phoebe, with her new martial arts skills, is able to kick and stab him with the blade and he dies. Piper and the Zen Master return to their proper bodies. The Zen Master accepts his mortality, despite his daughter's plea to let Leo save him. He reflects on the recent loss of Prue that the Halliwell sisters experienced, and explains to them that death leads to rebirth. It's a part of life, and a transition that everyone must go through. Limbo then returns to a place of beauty as natural order has been restored.
After defeating Yen Lo, Paige realizes the importance of knowing what the potions are and how to do them correctly, so she studies and is able to answer all of Piper's questions correctly.