Cole and Phoebe spar in the basement of the manor. Piper has been drawing up quizzes for Paige to answer, and Paige is bored. Phoebe says that Paige needs to get up to speed in a hurry. Cole warns Phoebe that The Source is facing threats from factions in the Underworld. The two then switch to sword-fighting; Cole thinks it'll help Phoebe learn to "fight like a demon".
Meanwhile, a Zen Master meditates in a garden. Behind him, Yen Lo draws his sword and stalks him; but An Ling jumps from a tree, sword in hand, and the two fight. An Ling turns out to be the Zen Master's daughter. Yen Lo had expected to succeed the Zen Master, and is angry that An Ling will instead. Yen Lo had turned to evil, and the master rejected him. They continue to fight, and An Ling severely wounds Yen Lo. Yen Lo jumps into a nearby water filled pool and disappears.
Piper quizzes Paige on making potions. Paige is distracted, and jealous that she's taking a boring quiz while Phoebe spars with Cole. Paige didn't study last night, because she was out, and she wants to go out with the boss's son tonight. Piper isn't pleased; she thinks Paige isn't taking her craft seriously. Meanwhile, in the basement, Phoebe thinks she's being pushed too hard.
The Zen master sends An Ling to another master to fetch the Dragon Blade. Yen Lo is in Limbo, where his wound will not advance.
Paige cooks a potion, which blows up and it switches hers and Phoebe's bodies. Cole is puzzled and Paige now runs out of the basement. She finds Phoebe in the kitchen and explains what happened. Cole comes up, still unaware of the switch.
An Ling enters a shop and asks for the Dragon Blade. The man behind the counter refuses to give it up. Piper enters the same shop looking for wormwood. An Ling jumps up and steals the Dragon Blade. Piper runs after An Ling. The master appears from the shadows, but before An Ling can give him the Dragon Blade, Yen Lo jumps from a puddle, stabs him, and carries him off to Limbo.
At the manor, An Ling explains to Piper and Leo that Yen Lo can cross to Limbo and back using water. An Ling can't do this, so Piper goes to the Book of Shadows to find another way.
Phoebe (as Paige) meets the boss's son, Mason, and they leave together; they go to the shop where Phoebe is looking for powdered toadstool. Paige (as Phoebe) bumps into Piper, who is still unaware of the switch. Each of Phoebe and Paige talks of herself, getting Piper's real thoughts on Paige. Training in the basement, Paige and Cole have a slight spat. Paige inadvertently speaks of Phoebe in the third person and Cole begins to catch on.
The Book of Shadows has no information on reaching Limbo, so Leo checks with the Elders.
Yen Lo enters the manor through some spilled water. As Phoebe returns, Yen Lo hides. Cole now realizes that Phoebe and Paige have switched bodies and purposely tries to make out with Phoebe (in Paige's body). Phoebe (in Paige's body) then flipped Cole over and Cole then revealed that he knows. Yen Lo attacks An Ling; she fights back with the Dragon Blade, but Yen Lo wounds her. She drops the Dragon Blade. The sisters fight him off and he disappears into the sink with the Dragon Blade.
During the fight, Paige tries to levitate, but ends up spinning in a circle. Piper demands to know what happened. Piper realizes the switch and scolds her sisters, but realizes that the potion could get one of them into Limbo. Phoebe and Paige make more of the potion and restore themselves to their bodies. Piper switches bodies with the Zen master, but the others realize too late that Yen Lo has the Dragon Blade.
Yen Lo quickly realizes Piper had switches places with the Zen Master and draws Piper's soul into the blade.
The Zen master, An Ling, Phoebe and Paige enter Limbo. Paige finds she can draw the blade to her hand without calling for it. She then orbs Piper's soul back to the master's body.
Meanwhile, the master is about to be drawn into a vortex, and Phoebe fights with Yen Lo. Paige orbs the Dragon Blade to Phoebe and she kills Yen Lo. Limbo turns from a stark landscape into a garden, and the vortex becomes a peaceful sky. The master and Piper are restored to their bodies.
The master tells An Ling that it is his time to die, and he enters the portal with the Dragon Blade, so Yen Lo too can be reborn. An Ling now knows how to leave Limbo, and the three sisters and An Ling return to Earth.
Piper and Paige stroll through a park. Paige liked the power boost she had in Limbo, and now studies her craft. They meet Leo and Phoebe, and when Cole shimmers in, he says he won't push her so hard to train any more and they shimmer off for a date in the South of France.