Cheerleading fever is sweeping the school and Buffy's caught the bug. Giles is not pleased, but Buffy reminds him that she successfully juggled both slaying and cheerleading at her old school, and she is sure she can do the same in Sunnydale.
At tryouts, Buffy chats with one of Willow's friends; fellow cheerleading hopeful, Amy. As they talk, they watch talented cheerleader wannabe Amber, complete her try out. Amy is staring at Amber, a jealous glint in her eyes. Suddenly, Amber bursts into flames! Buffy grabs a large piece of cloth, runs over to the girl, and douses the fire.
In the library, Buffy and the gang try to figure out what could have caused the girl to catch on fire. They consider spontaneous combustion, but dismiss the notion, when they realize that rage is usually the cause of the phenomenon.
The next afternoon, cheerleading tryouts recommence. Amy is doing well during a group tryout, until she flubs a cartwheel, knocking Cordelia over in the process. Moments later, Buffy finds Amy staring sadly at a cheerleading trophy her mother, Catherine Madison, won years earlier. They talk a bit and Buffy tries to reassure Amy that she does not need to live up to her mothers' standards.
When the squad is posted, Xander comes to Buffy and Amy with the news that Buffy made first alternate and Amy third. Sad but philosophical, Buffy tries to cheer up crushed Amy on what she feels is a defeat. Her attempts fall flat and Amy rushes off. Somewhere else, a cauldron bubbles with green liquid and a dark voice intones an evil spell. "Let your blackness crawl beneath my skin." the voice begs. "Accept thy sacrifice, Cordelia. Feed on her."
The next day at school, Buffy notices that Cordelia is behaving strangely: she is much less coordinated than usual. During drivers' education, she loses control of the car and crashes. Confused and disoriented, she wanders out into the middle of the road. Just as a truck is about to hit her, Buffy rushes up and knocks her out of the way. When Cordelia looks up, her eyes have gone completely white: she is blind.
When Buffy tells Giles about Cordelia's ordeal, he tells her that he believes that they are dealing with a witch. "First vampires, now witches," Xander scoffs, "No wonder you can still afford a house in Sunnydale."
The gang realizes that Amy is their most likely suspect, but how to prove it? Giles says that a test exists that can identify a witch. A potion placed on a potential witch's skin will turn blue, if the test is positive. In chemistry FORBIDDEN Willow mixes up the potion, and Buffy administers it by spilling it on Amy "by mistake." The potion proves positive just as another cheerleader's mouth disappears. Buffy backs away from Amy, staring at her in consternation. Amy looks back with an unreadable expression.
At home that afternoon, Amy arrogantly orders her mother to do her homework, who stands there meek and submissive. Clearly, her mother is afraid of her. Amy says she has something to do and then reveals Buffy's bracelet, clutched in her hand. Clearly, Buffy is next on her list.
With one cheerleader out, Buffy is called to replace her. At her first practice, Buffy is cheering almost drunkenly; full of pep, but with none of the self-possessed grace of the Slayer. Xander and Willow come into the gym just in time to see Buffy dismissed from the squad. "Amy," says the squad captain, "you just made cheerleader." Buffy nearly reveals her witchy secret, but Xander covers her mouth and leads her out of the gym.
Soon Buffy's pep turns to flu-like weakness. Willow wants to take her to the hospital but Giles knows that traditional doctors cannot help her. "This is a blood-stone vengeance spell," he says worriedly. "It hits the body like a quart of alcohol and then eradicates the immune system." Giles knows that the spell is deadly and they only have three hours to reverse it before Buffy dies. He tells them that the only way to reverse the spell is to get the witch's spell book or else decapitate Amy. Buffy is unwilling to kill Amy and suggests that she and Giles speak to Amy's mother: maybe at her house they can retrieve the book. Xander and Willow remain at the school to keep an eye on Amy.
When they arrive, Buffy realizes that Amy's mother, Catherine, is actually Amy. Amy confesses that her mother switched their bodies. Giles finds the witch's casting room and steal her spell book. Buffy and Giles devise a plan that will both save Buffy and return Amy to her rightful body.
Back at school, Catherine-as-Amy is in the gym, cheering with the rest of the team. Meanwhile, Giles is in the science lab, reading out of the spell book. For a few moments, Amy and Catherine start seeing out of their correct eyes. Realizing that something is amiss, Catherine-as-Amy leaves the gym to find the source of the spell. Wielding an axe, she forces her way into the lab and marches towards Buffy's prone figure. Just as she is about to strike a deadly blow to the weakened Slayer, Giles completes the spell. Mother and daughter are back in their correct bodies and Buffy's strength returns.
Naturally, Catherine is livid. Ranting and raving, she slams the axe into a lab table. Raising her hands in the air, she calls out for the dark gods. The spell fires toward Buffy, but she deflects it with a mirror. But the spell has to go somewhere. It ricochets off the mirror and back into Catherine's body, who disappears.
Afterward, Buffy and her mother have a short conversation. Buffy asks her mother if she ever wishes to be sixteen again. She is comforted to hear that her mother would never want to be a teenager again. "I love you, Mom," she says, dropping a kiss on her cheek. Joyce is confused. "I don't get it," she sighs.
The next day at school, Buffy and Amy walk through the school hallways discussing their adventure. Amy is thrilled to be living with her over-protective father. The girls have a run-in with Cordelia, whose eyes are back to normal. Cordy makes a snide comment about the girls' alternate status on the squad, but Amy is far from sorry. The real Amy never did want to cheer. "I know that I'll miss the intellectual thrill of spelling out words with my hands," she says.
Moments later, the girls stop in front of the trophy display case, where Catherine's trophy proudly stands. She doesn't know where her mother disappeared too, but wherever she is, Amy knows she won't be coming back. "That last spell? She said I'd never make trouble again," Amy says. "Wherever she is, I don't think we'll have to worry." She stares at the trophy for only a moment longer, and walks away. As the girls move off, a low groan escapes from the cheerleading trophy, and the eyes move frantically. It appears that Catherine is now forever ensconced in the very thing she sought – the perfect cheerleading figure.