Piper keeps receiving letters from Dr. Williamson, who treated Piper for Oroya fever in "Awakened". He wants her to come in for blood work. Piper has thrown all the letters away. Phoebe finds her granola box empty and in the trash; Leo, it seems, likes granola. Phoebe suggests setting some ground rules for what Leo can and can't do. Prue enters and announces she has a photo session with actor Evan Stone, and Phoebe is impressed but Prue, perhaps burned by her experience with Finley Beck ("Chick Flick"), wants to know nothing about him in advance. She wants to enter, shoot and leave. Piper asks if Prue thinks Leo lives there, and Prue agrees. Piper suggests that maybe they need ground rules after all.
Dr. Williamson has three caged monkeys, each with the name of a Charmed One. He is on the phone with Dr. Jeffries, who has yanked funding for his universal-antibody project, but he is not giving up. He has injected each monkey with a sample of the sisters' blood; he tries again, the monkeys become agitated, and monkey-Prue flings a syringe into his neck.
Dr. Williamson patches his neck up as the monkeys become more agitated. He tries to shush the monkeys and inadvertently flings several vials of blood into the wall, where they shatter. Dr. Jeffries enters and Dr. Williamson freezes and then unfreezes him. Dr. Jeffries suggests that Dr. Williamson take some time off. Dr. Williamson's sister has been in the hospital for some time, and Dr. Jeffries thinks it's been weighing a lot on him. When Dr. Williamson again demands contact with the Halliwells, Dr. Jeffries orders him to clear out the lab.
Prue goes to her photo shoot and meets Evan Stone. His publicist, Lucy, calls for security. She's had to shoo away several tabloid photographers in the last week. Prue hands over her ID and, since it's temporary, Lucy has to call 415 to confirm it.
Leo orbs into Piper's room. Thinking Piper is in there, he asks her about sex--but it's really Phoebe. They promise not to breathe a word to anyone. Phoebe pulls out a piece of paper and writes another ground rule--"no orbing in unannounced."
Dr. Williamson calls Piper and asks her to come in. She tells him no, and hangs up. In frustration, he telekinetically flings a computer against the wall. Leo comes into the kitchen; he hoped they could spend Piper's day off together.
Nurse Jordan calls Dr. Williamson into his sister's ward. Monkey-Prue astral-projects into Prue's photo shoot; she points the monkey out, but astral-monkey-Prue disappears before Evan can see. Prue quickly ends the session. Evan brings out her car keys, which she drops. As both bend down to pick them up, a tabloid photographer starts taking pictures.
Prue returns to the manor and finds that Evan has sent flowers. She tells Piper and Phoebe about the monkey, but they don't believe her at first. Prue mentions the rose on the hospital wristband; it's the same as the logo for San Francisco Memorial Hospital, where Dr. Williamson works. The sisters suspect that Dr. Williamson is on to them and Prue and Phoebe go to the Book of Shadows. Leo gets an important jingle and orbs out.
Dr. Williamson is in the ward with his sister and her husband Larry, a San Francisco cop. The sister is waiting for a kidney transplant and Larry is frustrated that she's at the bottom of a waiting list, while criminals get released on technicalities. Dr. Williamson puts a hand on the cop's shoulder and has a premonition of Larry having a heart attack. He calls for a crash team. Seconds later, Larry collapses. Dr. Williamson goes to the records room and wants a list of criminals who have recently been released from the jail ward.
The sisters find Dr. Williamson's lab and the monkeys. Phoebe thinks monkey-Prue was trying to warn Prue of what was happening. Piper notices voluminous files with their names on them on Dr. Williamson's desk. Prue notices he's run numerous tests on their blood. Suddenly, monkey-Prue waves a hand and a banana floats through the air. Monkey-Piper freezes it in midair. The sisters are horrified; they think Dr. Williamson knows they're witches. Phoebe takes hold of monkey-Phoebe and has a vision of Dr. Williamson blasting the vials off the table with Prue's power. Piper fears that if this is true, Dr. Williamson will have them quarantined again.
Dr. Williamson blasts down the door of a drug dealer, Benny Ritter. Benny pulls his gun, but Dr. Williamson flings him across the room. He sedates Benny and cuts out a kidney.
The sisters try to hustle the monkeys and Dr. Williamson's records out of the hospital. On the way out, they see the "kiss" between Prue and Evan on TV and overhear Nurse Jordan telling a secretary of Dr. Williamson's premonition. They go to the records room and find Dr. Williamson's request for the jail patients. They print a copy.
The sisters meet Darryl at Benny's place. Benny's assailant obviously had medical training; the wound was expertly stitched up. The sisters tell him only that it's supernatural and ask him to keep it quiet.
Prue tries to tell Gil Corso that she isn't dating Evan. The monkeys run loose at the manor and Phoebe has trouble dealing with them. Piper can't find anything in the Book about mortals or animals having powers. Suddenly, they see flashbulbs popping; photographers have mobbed the manor. Leo orbs back in and tells the sisters that mortals can't handle having powers in them. Unless they can get them out of Dr. Williamson, they'll drive him mad. His need to do good could well backfire. Phoebe starts working on a power-stripping potion. Photographers mob the manor and so Piper freezes them to allow Prue to escape.
Prue meets Evan and asks for help with the photographers. He advises her to let the whole thing blow over. At last Evan takes Prue's cell phone and calls Celebrity Peepshow, posing as a tipster named Julius. He promises to tell them that he dumped Prue, in line with his bad-boy image.
Dr. Williamson cuts out the heart of Frank McNamara, who has sold guns to children.
The photographers leave, much to Piper's relief. Phoebe slips the potion into milk bottles for the monkeys. She has monkey-Prue try to draw a banana to her. The monkey manages to get the banana out of Phoebe's hand, but before it can get to the monkey, she loses Prue's powers. Darryl comes to the manor and says Dr. Williamson has gone after two other people released from the jail ward--McNamara and Arlen Jackson. More seriously, he isn't bothering to stitch up his victims anymore, but leaving them to die. Darryl thinks that he may have to kill Dr. Williamson, but Piper fears Dr. Williamson might kill him. Piper pulls out the list from the hospital, and notices the last name on the list is Sally Dopler.
At a warehouse, Sally is working on something when Dr. Williamson walks in on her. Suddenly, he goes flying across the room. The sisters walk in. Piper tries to tell Dr. Williamson that he's hurting people, but he won't listen. Piper offers him a potion and tries to convince him to drink it. Instead, he flings both Piper and Prue across the room. Phoebe offers to help, but Dr. Williamson won't listen. Phoebe punches him several times and gets ready to kick him, but Dr. Williamson sends her flying. He smashes the potion bottle as he walks away.
The sisters try scrying for the doctor, but since he has their powers, they find only themselves. Prue and Phoebe think that they might have to kill Dr. Williamson, but Piper is reluctant to use magic on a mortal. Leo hasn't been able to find anything in the Book. Just then, they finally find Dr. Williamson. They meet him in a trash-strewn ally with junkies everywhere. Dr. Williamson tries to throw a scalpel, but Prue flings it away as the junkies flee. Dr. Williamson flings a saw blade, but Piper freezes it. She tries to freeze Dr. Williamson as well, but he fights through it. Dr. Williamson flings another saw blade, but Prue repels it and makes it spin in one spot. Dr. Williamson and Prue fight for control of the second blade. Finally, on Prue's cue, the sisters duck out of the way while she sends the second blade flying in another direction. The first blade unfreezes, bounces off the fence and into Dr. Williamson, killing him. Piper runs to him and starts crying over his corpse.
Back at the manor, the sisters burn Dr. Williamson's records of them. Phoebe has compiled a wish list for "someone as great as Leo". Piper, in turn, burns Dr. Williamson's letters to her; she feels responsible for his death. Piper goes upstairs crying for him; Leo orbs in and comforts her.