Holtz having failed in his mission to kill Darla and Angelus is contacted by the demon (?) Sahjhan to awaken in 2002 to take his revenge there. Some years later Angelus trains a young vampire named Penn who later becomes the LA serial killer The Pope. Then a little later Angelus kills a young man at Christmas time the day before his wedding (no wonder he was one of the most feared vampires). Then just as it seems were veering off course we are introduced to Drusilla as Darla presents her to Angelus from afar - then what we assume must me a day or two later he pretends to be her priest and begins his mental torment... OHHHHHH.
Side note: I decided to leave out Angelus' meeting with The Beast (which would have featured somewhere in ep5) because the way they did it was really choppy and wouldn't have made any sense if I had included it, I felt leaving it out was OK because seeing just the flashbacks it isn't really a key part of his history.