on Sunnydale High's graduation day. Although Faith initially works well with Buffy, she becomes increasingly unstable after accidentally killing a human and forms a relationship with the paternal yet manipulative mayor. The rivalry between Buffy and Faith eventually lands Faith in a coma. At the end of the season, after the mayor becomes a huge snake-like demon, Buffy, Angel, the Scooby Gang and the entire graduating class destroy him by blowing up Sunnydale High. At the end of the season, Angel and Cordelia leave the series to star in the spin-off series, Angel. 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 that prevents from harming humans. Every time he tries to harm a human, he suffers excruciating pain. He begins to fight on the side of the Scooby Gang, purely for the joy of fighting, upon learning that he can still 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 graduate student and US Army Ranger seconded to The Initiative. Although appearing to be a well-meaning anti-demon operation, The Initiative's sinister plans are revealed when Adam, a monster secretly built from parts of humans, demons and machinery, escapes and begins to wreak havoc on the town. Adam is destroyed by a magical composite of Buffy and her three friends, and The Initiative is shut down. During season five, a younger sister, Dawn, suddenly appears in Buffy's life; although she is new to the series, to the characters it is as if she has always been there. Buffy is confronted by Glory, an exiled Hell God who is searching for a "Key" that will allow her to return to her Hell dimension and in the process blur the lines between dimensions and unleash Hell on Earth. It is later discovered that the Key's protectors have used Buffy's blood to turn the Key into human form – Dawn – concurrently implanting everybody with lifelong memories of her. The Watchers' Council aids in Buffy's research on Glory, and she and Giles are both reinstated on their