This ghostly episode starts out at The Bronze where Buffy rejects the advances of a boy who's looking for a date for the Sadie Hawkins dance. She checks in with Giles at school, but first stops a male student from almost shooting a female student. They have no recollection of why they were fighting, and the gun disappears. Principal Snyder blames Buffy for the incident. While waiting in his office, a yearbook from 1955 falls off the shelf. Willow gives Giles a rose quartz that she found in Ms. Calendar's desk. In class later that day, Buffy starts daydreaming about a relationship a student had with his teacher. As she comes back to the present, she finds that the teacher has unknowingly written "Don't walk away from me, bitch!" on the chalk board. Then Xander is grabbed by a monster arm inside his locker. Buffy helps him break away, but the arm then disappears.
Giles is intrigued by the possibility of a poltergeist. Meanwhile, Angel, Spike and Drusilla have taken up home in a mansion where Angelus taunts Spike and flirts with Dru. Later that night, Giles witnesses the result of another argument in the school halls. The janitor shot a teacher who then fell over the balcony of the school, though only moments earlier they were cordial. Giles is convinced that Jenny is haunting the school.
Willow finds information on her laptop about a killing in 1955 where student James Stanley killed his teacher Grace Newman after she tried to break off their affair. In the cafeteria, chaos erupts as they find that the food has all been turned to snakes. The room empties quickly, and Cordelia is bitten on the face by a snake. Outside, Snyder talks to a man about the incident and reveals his knowledge of the Hellmouth. The principal is cowed by a mention of the mayor.
Willow devises a plan to contain the spirits, and they head off to the school where they prepare, though Giles has already arrived and is trying to summon Jenny's spirit. Buffy hears music coming from the Music Room and goes to see Grace and James dancing there. James' face suddenly changes to a gory mess, startling Buffy. Cordelia looks in the mirror to find her face has turned a gory red color. On the stairwell, Willow begins to sink into the floor, and Giles rushes to save her. Willow finally convinces him that the spirit is not Jenny. Everyone lights their candle and starts chanting the spell, but the candles blow out and a swarm of wasps enter the school. Everyone rushes out to find the school surrounded by wasps.
In the garden of their new home, Dru gets a vision about Buffy meeting with death. Tears just about pool up in Spike's eyes as Angelus holds Dru tight against him. Everyone recuperates at Buffy's while Buffy continues to show her anger towards James. She rushes off to the kitchen where she finds a sign for the 1955 Sadie Hawkins dance in her pocket. She heads to the school, where the wasps part for her to enter. Willow finds the ad and everyone rushes after Buffy, but they cannot enter the school.
Angelus appears in the halls as Buffy, now possessed by James, talks to him as if he were Grace. They continue the ghosts' argument with Angelus playing the role of Grace. At the climax, Buffy pulls out a gun and shoots Angelus. He falls off of the balcony as though dead. James (still in Buffy's body) rushes off to the music room where he plans to kill himself. Grace (still in Angelus), is not killed by the bullet. She wakes up and proceeds to the music room just in time to stop "Buffy" from pulling the trigger. They exchange apologies and kiss. The spirits, now able to pass on, leave their bodies. Buffy and Angelus break away from the kiss and Angelus realizes what he has been doing. Throwing Buffy aside, he rushes off.
At the garden, Angelus scrubs furiously at his body, knowing how close he had been with Buffy. He then invites Dru and Spike out to feed, knowing that Spike is using a wheelchair, so Spike remains behind. When they're gone, Spike stands up and kicks the chair aside, revealing to the audience that he has healed from his spinal injury.