At the end of season three of Buffy, Angel leaves Sunnydale and moves to L.A. where he continues to fight evil, only hidden away in the dark, pulling himself away from humans. Enters Doyle, a half demon with visions or people in danger. He tells Angel that he is his link - not only to The Powers That Be, but also to humanity.
They team up to save a young woman from a well established vampire in town. While they fail, they encounter Cordelia - who left Sunnydale for L.A. with big dreams of becoming an actress - and she ends up joining the team as well - at least until her acting career kicks off, she warns them.
While Angel following the same codes and rules as the Buffyverse, the show itself it quite different, a lot dark and more mature. Characters who were once shallow and comic relief on Buffy become deep, layered and complicated individuals. As the show evolves, Angel must fight his own demons, come to terms with his past actions and figure out his part in the greater scheme of things.