Luke (Brian Thompson) is about to finish off Buffy, who is trapped in a stone coffin, but she repels him with the silver cross that a mysterious stranger (David Boreanaz) had given her earlier that evening. She then escapes the mausoleum and saves her new friends Xander (Nicholas Brendon) and Willow (Alyson Hannigan) from vampires in the graveyard. However, Darla (Julie Benz) has already taken Jesse, and she and Luke now inform The Master (Mark Metcalf) about Buffy's unusual fighting abilities and knowledge of the supernatural, and it is suspected that she may be a new Slayer. The Master decides to use Jesse as bait.
Giles (Anthony Stewart Head) and Buffy give Xander and Willow a brief introduction to the world of vampires, demons and Slayers. Willow accesses the city council's plans for Sunnydale's tunnel system, and Buffy realises that there must be a means of access to it from the crypt where she fought Luke and Darla. Willow expresses her "need to help" now that she knows about the supernatural, and so continues assisting Giles with research. Xander, however, is hurt when Buffy declines his help in physically tracking down Luke.Willow is researching the Master in the computer lab when she overhears Cordelia (Charisma Carpenter) badmouthing Buffy, and is then insulted herself when she attempts to defend her new friend. Willow exacts revenge by convincing the computer-illiterate Cordelia to press the DEL key to "deliver her assignment", thus deleting it from the system.
The dark stranger appears again just as Buffy is about to enter the tunnel system in the crypt, and tells her his name is Angel. He gives her directions to The Master's lair, but pointedly refrains from wishing her luck until after she is out of earshot. Xander catches up with Buffy in the tunnels, having decided to follow her anyway despite her earlier discouragement. They find Jesse seemingly alive and unhurt, but he leads them to a dead-end in the tunnel system and then reveals that he has already been turned into a vampire. Buffy and Xander barely escape, with Xander having to pull Buffy out of a manhole and back into the safety of daylight while a vampire's hand tries to pull her back.Underground, The Master is unhappy about their escape and punishes the vampire Colin by violently poking his eyes out. Luke then drinks the Master's blood, turning Luke into "the Vessel". Back at the library, Giles explains that The Master arrived in Sunnydale 60 years ago to open the Hellmouth - a portal between this reality and another, demonic reality which, if opened, will allow demons to invade the Earth - but he was swallowed by an unexpected earthquake and is now trapped in a church that was buried underground. Tonight is a once-in-a-century opportunity called The Harvest in which, by allowing Luke to drink his blood, The Master will now gain strength from each victim's blood which Luke drinks that night until he is powerful enough to finally break free from his underground confinement. To prevent this, Buffy and her gang of friends must kill the Vessel. They wonder where Luke might attack so as to ensure the optimum number of victims, and Xander suggests The Bronze.
On her way there with the others, Buffy stops by her house to pick up some additional weapons before the fight, but is promptly grounded by her mother, who has received a call from Principal Flutie about Buffy skipping classes and is now terrified that the same events which led to Buffy being expelled from her previous school are happening again. Knowing that she cannot abide by her mother's wishes, Buffy collects her weapons from a secret compartment in a chest (the top layer of which is filled with stereotypical girlie items so as not to arouse suspicion) and climbs out of the second-floor window.
Luke and other vampires burst into The Bronze to begin feeding. Buffy arrives just in time to save Cordelia, who was newly attracted to Jesse because of the greater confidence he had gained as a vampire. Buffy notices the Vessel mark on Luke's forehead, and begins to fight him. Xander confronts Jesse with a stake, but is spared the choice of either killing or being killed by his former best friend when a fleeing woman accidentally pushes him into Jesse so that the stake pierces the vampire's heart. Darla knocks Giles to the ground and is about to bite him, but Willow saves him by pouring holy water on Darla. Buffy smashes a window so that extra light pours into the room, and Luke is momentarily stunned because he thinks it is daylight, allowing Buffy to stake him and so prevent The Master from rising. Angel watches as the now-leaderless vampires flee from The Bronze; he is clearly impressed by Buffy's success.The next morning, despite Xander's expectation that "nothing will ever be the same", Cordelia exemplifies Sunnydale residents' typical state of denial when it comes to the paranormal. Giles warns Buffy and her friends that the Hellmouth will continue to act as a magnet for demonic forces and so many more battles will lie ahead, which they accept more nonchalantly than he would like.