Buffy The Vampire Slayer - The Lost Slayer parts 1, 2, 3 & 4 - Prophecies; Dark Times; King of the Dead; Original Sins

Buffy's worst enemy is closer than she things. Her most frightening nightmares have become a reality. She faces an adversary who was once her most trusted mentor. Can Buffy defeat a foe who not only knows her techniques, but helper her develop them?