The students of Sunnydale High School are spending the afternoon at the zoo. Besides it's standard zoo animals, the facility has a special new hyena exhibit, marked 'Positively NO Admittance' The piques the interest of Sunnydale's obnoxious cool crowd, who had already had their fun tormenting Buffy and shy student named Lance. After grabbing poor Lance's notebook, they enter the forbidden hyena house forcing him to follow. Xander, worried about his classmate, decides to come to his rescue. As they wait for Xander, Buffy and Willow meet an eccentric zookeeper, who claims the hyenas can understand human speech - they learn people name's, call out to them and then eat them. Meanwhile, the crowd in the hyena house starts to get rough with Lance, but suddenly their eyes start flashing yellow - apparently they've stepped into a mystical circle on the floor and a transformation has taken place.
Back at school, Principal Flutie proudly introduces the students to Herbert, the Sunnydale Razorback's new mascot. Not quite as menacing as the team's namesake, Herbert is actually a little pig. Xander elicits a strange reaction from Herbert when the two exchange a glance. Since returning from the zoo trip, he is more confident, more aggressive and generally not the same old Xander. His love-sick puppy stares have turned to animal stares - he has even taken to sniffing Buffy.
Willow brings the news to Buffy and Giles that Herbert is dead - the pint sized porker has been eaten by the hyena possessed students. Buffy tries to confront Xander, but he becomes even more aggressive and pounces on her. They scuffle for a while, but Buffy finally decks him, and locks him into the steel book-return cage. When it's discovered that the pack is responsible for Herbert's demise, Principal Flutie is up in arms? He summons the group to hi_s office to reprimand them, but doesn't get a chance.
The news horrifies everyone - Principal Flutie has been eaten! The official story is that a pack of wild dogs did it, but Buffy, Willow and Giles know the truth. Since Xander was with Buffy when the incident occurred, she is relieved that he was not involved. Giles has figured out that in order to restore the pack, the spirits of the hyenas must be taken from the students and put back into the animals. While Buffy and Giles go to the zoo, Willow offers to watch Xander. The zookeeper, well-versed into these matters, offers to help with the transformation and says that all the students must return to the mystical circle in the hyena cage. But one member of their pack is missing - Xander - and Buffy and Giles realise, to their horror, that they will seek him out, leaving Willow vulnerable to their attack. When they do just that, Xander breaks free from the cage, but Willow hides. They escape the school grounds and Buffy leads them to the zoo.
While everything seems to be going according to schedule, it turns out that the zookeepers plan is too absorb all the hyena's spirits himself. He does and grabs Willow in order to perform a predatory act which is part of the ritual. Xander, back to his own self, reacts to seeing his friend in joepardy and dives on the zookeeper, freeing Willow. When the zookeeper goes after Buffy, she hurls him into the hyena cage, where he's promptly devoured.