Frankfurt: a young punkish girl sprints frantically through the city, chased by two robed baddies whose gleaming daggers look familiar. They catch her, killing her instantly. They depart, but the girl opens deadened, vacant eyes and says, "From beneath you, it devours." At that moment, Buffy awakens from a nightmare about the dead girl, and echoes her final words. She knows there are other girls out there like her, dying, doomed.
The next morning on their way to Sunnydale High, Xander, Buffy and Dawn discuss Buffy's new gig. When the Slayer asks her new employer how she got the job without college credentials, he responds that the students need someone they can relate to, and she is it. She sets off in an unsuccessful search for Spike, who earlier that morning had been ranting and raving in the school basement, terrified of something he couldn't see.
Willow prepares to leave England, and while she's afraid of screwing up again, she's more frightened that her friends will reject her. Giles does his best to convince her it's time, and she goes on her way.
That night, a young woman, Nancy, walks her dog, only to have it unceremoniously sucked into the ground by a big and growly worm. Screaming, Nancy takes off running and literally bumps into Xander, who brings her to Buffy's. They make a plan to go after the thing, and Spike appears in the doorway, prepared to lend a hand. It's strange--he looks totally normal, well dressed, good hair, the works. He lets it slip that Buffy has already seen him back in town, and Xander and Dawn are livid.
Buffy knows she needs Spike's help, so she hesitantly accepts, and sends Xander to take Nancy home. Buff and Spike check out the hole where the dog got munched, and Buffy is clearly spooked, remembering Spike's attempted rape. She can't forgive him, but senses something different about him. He doesn't fill her in on the whole soul thing, but does say that whatever ate the dog is long gone.
After Xander walks Nancy home, the two start making eyes at each other when that pesky worm returns and rips open the floor to attack. They make a break for it, running high enough up some stairs so the worm can't get to them. Nancy starts to crack, complaining that things can't get much worse, especially after her recent breakup with an abusive boyfriend, Ronnie.
Xander has a thought, and asks if Nancy has done any wishing lately about the guy. Turns out she did, and Anya's to blame for turning Ronnie into a worm. The gang (plus Nancy) confronts the demon at the Bronze, but she is unapologetic for having turned him not just into a teeny tiny worm, but a giant Sluggoth Demon.
When Anya looks at Spike, she sees something new: a soul. To keep her from revealing his secret, Spike hauls off and punches Anya more than once, and both their demon faces are revealed. Buffy breaks in and pummels Spike in return as he taunts her for taking out her repressed anger on him. Before she can do any real damage to the Vamp, Xander realizes Nancy is gone, and Buffy takes off after her.
On the street, Nancy is going home when the worm comes tearing after her, and Buffy (with Spike following) literally swings to her rescue. Spike prepares to spear the worm, but there's only one problem: at the moment he stabs the thing, Anya reverses the spell and the worm turns back into a very human Ronnie. Since his chip is still in place, Spike cries out in pain after harming the human. He loses it, practically switching personalities as Buffy calls for an ambulance to tend to Ronnie's injury. Spike warns of the Big Bad coming, repeating, "From beneath you, it devours." He takes off, and Buffy trails him wondering what's up.
She finds him at a church and, through his ravings, deduces he's gotten his soul back, all for her. Now Spike is dealing with the guilt from his past, compounded by voices in his head, and the voice of the demon that's coming. He wants to rest and slumps against a cross. Buffy watches as the smoke rises from his burning skin.
Summary from Buffy.com