Angel (season 1)
At the end of the third season of "Buffy", the 242-year-old, re-ensouled vampire Angel left Sunnydale to give teenage Slayer Buffy Summers the chance to live a normal life. Angel is now living in the big city of Los Angeles. With Buffy gone Angel is now completely cut off from society, every day getting closer and closer to giving in to his vampiric hunger. It's not until he befriends the half demon and fellow Irishman Doyle, who is sent visions of people in trouble by The Powers That Be, and fellow Sunnydale resident Cordelia Chase, who grounds Angel's life in the humanity around him, that he truly begins to take charge of his life and seek atonement for his past sins. He sets up his own detective agency, Angel Investigations and begins to "help the helpless".
The Yoko Factor
Still upset about what happened between her and Angel during her visit to Los Angeles (in the "Angel" crossover episode "Sanctuary"), Buffy returns from L.A. to her empty dorm room. Xander brings Riley some clothes, and they talk about their mutual distaste for Angel, Riley having been told by Buffy about her previous relationship with him. However, it emerges that she has not told him the whole truth; while Riley was aware that Angel lost his soul and became Angelus, Xander tells Riley that having sex with Buffy was the trigger that set Angelus free.