"Dig a bit into the history of this place," as librarian Rupert Giles explains to Buffy,
 "You'll find there've been a steady stream of fairly odd occurrences." The area is a
 center of mystical energy. And all the signs point to a crucial mystical upheaval. Some
 sixty years ago a very old, very powerful vampire came to this southern California town,
 and not just to feed. The Spanish who first settled the area called it Boca Del Infierno --
 roughly translated, "Hellmouth" -- a sort of portal from this reality to the next. This
 Master Vampire hoped to open the portal and bring the demons back. And destroy the
 world of Man.

 "But," as Buffy's new friend Willow Rosenberg adds, based on her own computer
 research into old city and county records, "he blew it. There was an earthquake that
 swallowed half the town. And him too -- or at least there were no more vampire-type
 killings afterward."

 "Opening dimensional portals," Giles adds, "is tricky business. Odds are he got
 himself stuck. Like a cork in a bottle."

 However, once in a century comes The Harvest: a night when a Master Vampire can
 draw power from one of his minions while it feeds. Enough power to break free, and to
 open the portal. The minion is called the Vessel, and he bears a three-pointed star
 symbol.