At Buffy's 19th birthday party, Giles finally realises that he is a middle-aged man hanging around with a bunch of teenagers and starts to get depressed about his life. He feels even more like the third wheel when he finds out about Riley and the Initiative, which Buffy neglected to tell him about. When Ethan Rayne returns to town, instead of kicking his butt back to England, Giles goes for a drink with him. The next morning Giles wakes up and notices that he has turned into a demon.
"Into every generation, there is a chosen one. She alone will stand against the vampires, the demons, and the forces of darkness. She is the slayer".
When a young vampire slayer by the name of Buffy Summers, moves to Sunnydale, California, she quickly finds out that Sunnydale is located right on top of the Hellmouth - the center for all evil activity. Her new watcher, Rupert Giles, also happens to be the school librarian. It is his job to train her and guide her in all the skills she needs to be a Slayer. She and a group of close friends, commonly referred to as "The Scooby Gang", help her in her battle against evil.