It's a terrific day to be out of school, except that Buffy and her Sunnydale High classmates are technically on a field trip to the zoo. A gang of four kids taunt and terrorize other students, and when one boy does not have the courage to tell Principal Flutie what they have done to him, they "reward" him by taking him with them to the Hyena House even though it is under quarantine. Xander follows to help him, whereas Willow and Buffy are stopped by a warden. He warns the two girls that the animals, fresh from Africa, are said to have special powers. They can even call your name.
In the Hyena House, the hyenas take a flashy-eyed look at the gang of four and Xander. Their eyes flash in return. Only the original victim is spared. None of them notice that they have been standing on a magic symbol of some kind.
Xander is now part of the gang, and his behavior has changed: he is insulting, cruel, tends to scratch himself and smell people. Even more ominous, the school's new mascot piglet Herbert tries to flee when it smells Xander. During dodge ball, Xander hits Willow with an excessively hard throw. The game ends with Buffy the last remaining member of her team and Xander, the gang of four and the victim from the Hyena House on the other side. Instead of attacking Buffy, the pack goes for the boy until Buffy steps in. Later, Xander tells Willow in front of the laughing gang that he won't be needing her help any more and is happy he won't have to look in her pasty face ever again. Buffy watches the exchange, but when she confronts him, Xander walks off with the other four, still laughing. Guided by their noses, the five pay a visit to Herbert's cage. Xander suggests lunch and the piglet squeals in terror.
Giles shows no inclination to believe anything is wrong with Xander except that he is a 16-year-old boy. His attitude changes when Herbert is found, eaten. After checking his books, Giles warns that they could be dealing with a case of possession. Buffy runs to find Xander, and finds the piglet's cage totally demolished. Xander jumps Buffy, pins her to the floor and tries to sexually assault her and he asks Buffy if she like Angel more than him because he's dangerous stating she likes danger. Buffy knocks him unconscious with a desk and locks him in the book cage in the library.
When Principal Flutie finds his pig dead, he knows that the original gang of four are involved and calls them into his office. There, they kill and eat him.
Returning from a teacher's meeting to the library, Giles tells Willow and Buffy about what happened to Principal Flutie. Giles and Buffy go see the zoo warden who tells them that he is not surprised by the possession and knows about the magic involved, but is not sure how the students were affected: he hasn't been able to figure out the ritual. Giles supplies the missing information: a predatory act is required, like when the original four students tormented the boy.
Meanwhile, in the library, Xander tries to sweet-talk his way out of the book cage, but Willow sees through his ruse. The other four pack members break into the library, free Xander, and then all five hunt Willow through the corridors of the school. Cornered in a class room, she is rescued by Buffy and Giles. The five turn away from Buffy, and find an easier target, a family in a car. Buffy drives them off there, too, and offering herself as bait, lures them back to the Hyena House where the warden in full war paint is supposed to perform a reverse of the possession spell with Giles' help. Giles realizes that the warden had tried to call the power for himself, but couldn't figure out how until he learned about the predatory act from Giles. The warden knocks Giles unconscious.
Willow reaches the Hyena House before Buffy, and the warden ties her up and puts a knife to her throat, telling her it is the "predatory act" that will trigger the ritual and save the boys. Buffy arrives with the others close behind, and stops in when she sees Willow in peril. The pursuing pack knocks her down, and the warden uses this predatory act to shout a spell that pulls the animal spirits from the five students into himself. His eyes flash and he tries to bite Willow. Xander, freed of the spell, sees Willow in danger and tackles the warden. In the fight, Buffy knocks the warden into the hyenas' pen, where he is eaten. The gang of four flee. When everything is over, Giles staggers in.
The next day, Xander tells Willow and Buffy he does not remember anything, and they shrug the whole episode off with a smile. Giles, walking up to him from behind, points out that he cannot remember reading anything about memory loss during possession in his books, but promises to keep the embarrassed Xander's secret.