 If the Hellmouth opens, demons will invade the Earth.Tonight is a once-in-a-century opportunity called "The Harvest" in which, by choosing one of his minions to drink The Master's blood and marking him with the ritual's symbol, the vampire king will draw strength from each of this minion's victims, until he is powerful enough to finally break free from his confinement and resume what he has started decades ago.To prevent this, Buffy and her gang of friends must kill the Vessel.