(Plot synopsis from the official Buffy website)
Giles has been roped into supervising Sunnydale's talent show. When Buffy, Xander and Willow stop by to tease him about it, the new principal punishes them by insisting they come up with an act.
One of the dancers in the show is found dead, with her heart removed. The last person she was seen talking to was Morgan, a strange, awkward student who is a ventriloquist in the talent show with his dummy, Sid. When Buffy tries to question Morgan, he gets nervous and rubs his head. Sid seems to have a mind of his own, and Morgan talks to him as if he were real. Still suspicious, Buffy goes to check out Morgan's locker, but finds only the empty puppet case. When Buffy goes to sleep that night, Sid is outside her window. She feels him enter the room but when she screams and turns on the light, he's gone.
The next day, Giles tells Buffy, Xander and Willow about a brotherhood of demons who need human organs to maintain their humanity. Although this sounds like Morgan may have killed the dancer for her heart, these demons have super strength, while Morgan has been growing weaker. Willow discovers a book which says that dolls and mannequins are capable of becoming human by harvesting organs. Buffy, looking for Morgan in the prop room, finds him dead, with his brain removed. A light rig suddenly comes crashing down on her, and Sid is next to her with a kitchen knife. They have each mistaken the other for a demon. Sid explains that he was a human, but then was cursed, and he thinks the demon who cursed him is in the talent show. If he can kill that demon, he'll be free. Backstage at the talent show, Morgan's brain falls from the catwalk apparently the demon has rejected it. Willow researches Morgan's records and finds out that he had brain cancer. This means the demon is still going to be looking for a healthy, intelligent brain.
We find Giles in the auditorium, innocently helping Marc, a student performing a magic act in the talent show. Marc convinces Giles to fill in for his assistant and lie down in a guillotine. Just as Giles realizes he's about to get his brains removed, Buffy runs in to save him. Marc changes into a demon, and Sid finally stabs him in the heart. Now that the demon is dead, the animated Sid turns back into a normal puppet. Suddenly, the curtain opens as a stunned audience attending the talent show looks at the dumbfounded gang on stage.