To prepare for Sunnydale High's cultural exchange program, Buffy visits an Incan exhibit with her schoolmates. She is paired with an exchange student with whom her mom signed her up. Xander becomes jealous when he learns that she will room with a guy.
After everyone leaves the museum, a class clown breaks the seal on a mummy while trying to steal it. The princess wakes up, for the curse is broken, and pulls the unfortunate student into her coffin. She mummifies him by a kiss on the lips. When the Scoobies rush to the museum, they encounter a sword-wielding guard and the remains of the missing student.
Buffy's exchange student arrives at the bus station, and the mummy girl sucks out his life, too. The 500-year-old becomes a beautiful teenager, and poses as "Ampata," the boy who was supposed to stay with Buffy (everyone simply assumes that the information was wrong on her gender). Xander is smitten with her, and the two begin a relationship. Giles asks "Ampata" to decipher the seal from her tomb, and she explains (reluctantly) that it describes a girl chosen to die to save her people, and a bodyguard who will keep her from straying from that path. She also tells Giles to destroy the seal completely; apparently it being rebuilt will end Ampata's life. This bodyguard appears again and again, trying to stop Ampata, until she finally manages to use her kiss on him in the bathroom, sucking out his life to keep herself from dying.
Xander asks Ampata to the dance to enliven her; she gladly accepts. Willow is downtrodden to find her crush with another girl when the guitarist (Oz) at the Bronze notices her. Meanwhile, Buffy and Giles open Ampata's trunk and discover the real Ampata's body. Giles tries to piece together the seal while Buffy tries to save Xander from Ampata's deadly kiss. But Ampata feels too much for Xander and leaves for the museum. She tries to stop Giles from putting the seal back together. Buffy saves Giles, then Ampata starts to deteriorate as she tries to feed off Willow. Xander shows up and insists that if she must feed on anyone, it should be him; despite Ampata's feelings for him, she is quickly deteriorating back into a mummy, and is willing to kill him to remain alive. Buffy shows up to fight her, saving Xander, and in the battle, she weakens to the point of returning to her dead form.