Leo returns to San Francisco to beg the sisters to protect a woman who is being stalked by a demonic stalker.
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.
The sisters' vacation is cancelled when Leo appears in the Halliwells house the victim of a Dark Lighter's lethal poison tipped-arrow. Leo is seeking the sisters help to protect a girl that is being targeted by the Dark Lighter. To try to save Leo from dying, Piper casts a spell that will switch her powers with his. Unfortunately the spell also causes Prue and Phoebe's powers to swap. Andy quits his job to help protect Prue's secret from being exposed by an Internal Affairs investigation.
Leo is shot by the arrow of dark lighter Alec who is obsessed by his charge, and ask the sisters to help protect them as he is being targeted by the dark lighter. Piper casts a spell to swap her powers with Leo's so she can heal him but the spell also causes Prue and Phoebe's powers to swap. Piper fails to heal Leo because she can't find what triggers his powers. Piper and Prue ultimately find the better way to kill Alec and save Leo. Meanwhile Andy leaves his job to help protect Prue's secret from being exposed by an Internal Affairs investigation, headed by one "Inspector Rodriguez".
While protecting the human and future white lighter Daisy, Leo is wounded by a poisoned arrow shot by the dark lighter Alec, who wants to seduce Daisy to procreate evil. Leo asks the Halliwell sisters to protect Daisy, and Piper casts a spell to swap the healing powers of Leo with hers, but accidentally Prue and Phoebe also switches their powers. The sisters have difficulties to handle their new acquired abilities, and Piper is unable to trigger the healing power. Meanwhile, Andy is having troubles with the Internal Affairs protecting Prue, and he is temporarily suspended from his duties.
- Daisy is startled entering her car, drops a bag and cuts her hand on broken glass. Leo appears behind her. Daisy is relieved to see him; she thought he was Alec, a Darklighter who has been chasing her for some time. Leo heals her hand, much to Daisy's amazement. Leo tells Daisy that he brought her to San Francisco, because he has "powerful friends" who can help protect her. He also tells her that he's made her invisible to Alec. At that moment, Alec appears. Daisy flees. Alec conjures a crossbow and shoots Leo in the shoulder. Leo orbs to the manor.
Prue and Phoebe are planning a vacation in Cabo San Lucas. Piper calls from the attic; she has found Leo with an arrow in his shoulder. Leo admits that he is really their Whitelighter. Leo warns Phoebe and Piper that the arrow is poison-tipped. Prue returns to the attic with several bandages, and uses her power to remove the arrow. Leo tells the sisters about Alec and Daisy. He was protecting Daisy, because she has been identified as a future Whitelighter. Alec was originally after Daisy to seduce her and produce Darklighter spawn. However,
they fell in love, until she found out what he was. Alec, like most Darklighters, has the touch of death. Andy and Darryl are together at their desk, when Prue calls Andy. Andy can't talk now, as Darryl knows he's hiding something, so Prue offers to meet at Quake. Andy tells Prue to be careful, as Internal Affairs is after him. Prue tells Andy about Daisy; he offers to review security cameras to find her. Leo is bandaged up, but the arrow's poison is slowly killing him, and he can't use his healing power on himself. With his powers fading, he is losing his ability to cloak Daisy.
Alec orbs into Daisy's hotel room and won't leave her alone. The motel manager knocks, and then unlocks the door. Alec kills the manager as Daisy flees through the fire escape. Andy and Prue arrive, and Prue flings Alec across the room. Alec orbs out but, unlike Leo, his orbs are black.
Piper has found a power-switching spell in the Book of Shadows, and thinks she can use it to switch her powers with Leo, so she can heal him. With Prue and Phoebe all present, Piper casts the spell. Kit walks in and Piper tries to freeze her, but can't. Suddenly, Prue touches Phoebe and has a premonition of Kit apparently knocking over a lamp. Kit walks up to the lamp and Phoebe tries to shoo her away, and in the process, flings the lamp into the wall, shattering it. Piper must have Leo's healing power, but she doesn't know how to use it. Prue tells Piper that she has to figure out how to trigger Leo's power, just like they had to find their triggers when their own powers were unbound.
Andy calls and says that Daisy has bought a bus ticket.
Inspectors Rodriguez and Anderson grill Andy about the scene in the hotel. Rather than answer, Andy turns in his badge and his gun.
Daisy reaches the bus station and finds Alec everywhere she turns. Prue and Phoebe walk in. Prue tries to goad Phoebe into getting angry; she knows that her telekinesis was originally triggered by anger. Finally, Prue remembers that during high school, several guys called Phoebe "Freebie", after they caught her making out under the bleachers; the insult causes Phoebe to knock some magazines off a rack. Prue has a vision of Daisy cowering in the ladies' room. Prue and Phoebe confront Alec in the ladies' room. Alec conjures his crossbow. Phoebe tries to fling it out of his hand, but only causes all of the taps to come on and all of the soap to squirt out of the dispensers. Prue admits that she hit Grams' car several years ago an accident for which Phoebe took the heat. Phoebe flings Alec into a stall. Alec drops the crossbow. Prue picks it up, takes aim and shoots, but Alec black-orbs away. The two sisters bring Daisy to the manor.
Andy has sent flowers to Prue and the card says he needs to see her. Prue leaves to meet with Andy, while Daisy and Phoebe go to the attic. They find Leo almost dead and Piper crying. Daisy tries to leave, but Piper convinces her to stay.
Phoebe tries using telekinesis on Alec but she hits the chandelier instead Andy tells Prue that he has turned in his badge and is suspended. He warns her to be careful, and that it's best that they not be seen together, lest Rodriguez find out that Prue is his source. Andy adds that Prue and her sisters are doing the very thing that made him want to become a cop. Piper, upset, cries over Leo's body. She has tried to heal him several times, but can't figure out his trigger. She collapses on his body and tells him that she loves him.
Suddenly, her hands start to glow, and Leo is healed. He tells her that love triggers his healing power, but she had to find that out for herself. They come downstairs and prepare to call Prue, when Alec black-orbs in. Phoebe tries to blow him out the door, but knocks the chandelier down instead. Alec grabs Piper and offers to spare her life, if the sisters let him have Daisy. Prue comes in behind him. Alec tosses Piper aside, grabs Daisy and black-orbs out. Leo feels too weak to use his powers, so the four leave their powers switched. Leo coaches Piper on how to sense a charge. Piper finds Daisy and Phoebe and Prue go after her while Piper stays with Leo. They find Daisy and Alec in a cemetery, where Alec is about to sacrifice Daisy. Phoebe flings Alec aside. Prue casts the power-switching spell, just as Alec is about to use his touch of death on Daisy. Suddenly, Prue's hand starts glowing red-hot; she has Alec's touch of death and realizes hate is the trigger for it. Phoebe draws Alec towardsPrue. Prue incinerates Alec with his own power and switches their powers back just before he dies. Prue says that she never had to feel so much hate before and doesn't want to ever feel it again.
The sisters and Leo switch their powers back. Leo, himself, had been an Army medic in World War II. He died in the war and was offered the chance to become a Whitelighter. He accepted, but would give it all up for life with Piper. However, Piper thinks that would be too much of a loss for him.
Andy and Darryl meet at a noisy construction site. Rodriguez and Anderson are watching and using a long-range microphone, but the noise makes the microphone useless. Rodriguez, however, hears Andy mention Prue. Anderson wonders how that's possible. Suddenly, Rodriguez' eyes turn fiery red and he sonic screams. The sound penetrates Anderson's earphones, and he falls dead on the steering column.
Piper puts on Leo's dogtags, while Prue and Phoebe mix tropical drinks to make up for not making it to Cabo.