01E21 - Love Hurts

A gravely hurt Leo appears at the manor, asking the Halliwell sisters to protect an innocent woman returning to San Francisco under his guidance. Daisy (Lisa Robin Kelly) is being stalked by a Darklighter who hunts and kills present and future Whitelighters with poisoned arrows. The Darklighter Alec (Michael Trucco) fell in love with her. Leo reveals that the Darklighter's poison is very deadly, and Piper finds an ability-switching spell in the Book of Shadows so she can use Leo's innate healing power on him. Unfortunately, this has the side-effect of switching everyone's respective abilities and they all have to try to learn to properly use them. While Prue and Phoebe manage to control each other's powers, Piper is unable to heal Leo and he dies. Afterwards, she admits her love for him and discovers that it is the trigger for his mystical ability and succeeds in healing him fully. She then tracks down Daisy, and Prue vanquishes Alec by utilizing his own magical ability against him.