A fight with a cowboy vampire who introduces himself as Lyle Gorch distracts Buffy from picking up a dress for her mother and thus lands her in the doghouse. "A little responsibility is all I ask," Joyce says, and that's exactly what Buffy gets: Mr. Whitmore, the Teen Health teacher, gives the class eggs to watch over as though they were babies, as a lesson in the consequences of sex. That night, Buffy enlists Angel's aid in hunting for Lyle Gorch and his brother Tector, but instead the young lovers wind up smooching as the Gorch brothers watch from afar. When Buffy goes to bed that night, a tentacle emerges from her egg and rests on her face.
The next day, Buffy and Willow are both unusually sluggish, and Willow reports that Mr. Whitmore didn't show up for school. Xander reveals that he hard-boiled his egg. That night it's more kissing instead of slaying for Buffy and Angel, and the mention of her egg project leads Angel to ask Buffy what she sees in her future. "When I look into the future," she replies, "all I see is you. All I want is you." Meanwhile a security guard discovers the door to Sunnydale High's basement open. Going down to investigate he discovers a huge hole in the wall. Mr. Whitmore comes up behind the guard and pushes him into the hole.
When Buffy returns home, she sees her egg twitching. Suddenly it breaks open, and a small, multi-legged creature springs out and attacks her. She manages to kill it and calls Willow to see if the same thing happened. Willow says her egg is normal, and Buffy hangs up, but then we see that Willow's egg has indeed hatched. Willow doesn't look quite herself. All the noise awakens Buffy's mother, who sees Buffy dressed at that late hour and draws the only obvious conclusion — Buffy gets grounded for the rest of her life.
Cordelia also claims ignorance, but when Xander almost eats his hard-boiled slimy thing they have a specimen to dissect. "It's possible Mr. Whitmore wasn't harmed," says Willow. "Maybe the offspring just used him to return to the mother bezoar." Before they can wonder how she knows that, or what a bezoar is, Willow and Cordy knock Buffy and Xander out and deposit them in a closet. Then, joining a parade of other possessed students, they grab shovels and picks and file down to the basement and through the hole. Meanwhile, Joyce arrives at the library to pick up Buffy, but only finds Giles, who makes small talk but then places a hatchling on her neck.
After coming to, Buffy and Xander find Giles' research: the bezoar is a pre-prehistoric parasite who takes control of its victims' motor functions. They trail the possessed students to the basement and find them all digging up the mother bezoar. Then the Gorch brothers show up — bad timing. Buffy and Lyle duke it out, then Tector gets himself eaten by the mother. Lyle blames Buffy and throws her to the ground, leaving her dazed long enough to be dragged down by the mother. A few audible kicks and punches later, the mother's eye closes for the last time, and Buffy emerges, covered in black ichor. Lyle runs away, everyone's possession is broken, and Giles tells everyone it was a gas leak. Joyce confines Buffy to her room, but that doesn't stop her from making out with Angel — with the help of a ladder.
