Season four sees Buffy and Willow enroll at UC Sunnydale while Xander joins the workforce and begins dating Anya, a former vengeance demon. Spike returns as a series regular and is abducted by The Initiative, a top-secret military installation based beneath the UC Sunnydale campus. They implant a microchip in his head which prevents him from harming humans. He reluctantly helps the Scooby Gang throughout the season and eventually begins to fight on their side after learning that he can harm other demons. Oz leaves town after realizing that he is too dangerous as a werewolf, and Willow falls in love with Tara Maclay, another witch. Buffy begins dating Riley Finn, a grad student who she later realizes is a member of The Initiative. Although appearing to be a well-meaning anti-demon operation, it is realized that it had more sinister plans as its demon/Human/computer hybrid secret project, Adam, escapes and begins to wreak havoc on the town.