The Scooby Gang discusses plans for Buffy's birthday and dealing with Glory. Giles reveals that Glory is the god of a demon dimension and in order to stay in human form, she needs to suck energy from humans, leaving them insane. The gang starts asking questions about The Key and Buffy finally breaks down and tells them the truth about Dawn. Several of the Knights of Byzantium chant around a fire before they are interrupted by one of Glory's minions. Glory arrives and destroys all of the Knights except one whom she later tortures for information.
At the Magic Box, Dawn feels awkward because of the way everyone is treating her and notices when Giles hides a book in a hidden counter drawer. Buffy opens presents from her friends and everyone gets quiet when she receives a framed picture of herself and Dawn (from a vacation which is, like most of Dawn's life, a false memory) from her sister. Dawn finally gets upset and confronts everyone about their strange behavior around her, then storms to her room.
After sneaking out of the house, Dawn runs into Spike, who was keeping his typical watch outside Buffy's house. After a brief conversation, Dawn tells Spike that she is on her way to the Magic Shop to steal a book.Spike notes the myriad dangers of roaming around alone at night, and then he accepts Dawn's offer to let him tag along. With Spike's assistance, Dawn breaks into the shop and finds the book that she had seen Giles hide earlier. By candlelight, Dawn and Spike read about the truth of Dawn and The Key. Spike treats this revelation with a peculiar equanimity; Dawn is less sanguine.
Dawn returns to the house, bleeding from a self-inflicted knife wound, tearfully questioning what she is. Joyce and Buffy try to talk to Dawn, but everything has changed for her and she's scared, so she demands that they leave her alone. Buffy initially blames Spike for letting Dawn find out the truth the way she did. He turns the tables on her and blames her for not telling Dawn the truth in the first place. He also notes that Dawn was going with or without him, and that he only went along to protect her from harm, thinking that she would be safer with "Big Bad" looking over her shoulder.
Jinx threatens Ben at the hospital, but Ben reveals that Glory can't hurt him, no matter what he does. After overhearing Buffy and Joyce talking, Dawn rampages through her room, burns her diaries, and runs away. The smoke alarm alerts Buffy and her mom to Dawn's little fire and departure.
The gang gathers at the Magic Box and then splits up to search for Dawn. Spike does what he can to comfort Buffy and tells her that they will find her sister before it's too late, and Buffy admits that Spike had been right about Dawn -- Buffy should have been honest with her in the first place. Dawn passes through the park, reliving past memories only to be reminded of their falseness, then ends up at the hospital.
She searches for answers in the Psych ward, trying to persuade the mental patients to tell them what they see when they look at her, then runs into Ben. She blurts out to Ben that she's The Key and he freaks out trying to make her leave before Glory can find her, but it's too late. Ben suddenly changes into Glory, but Glory remembers nothing about Ben's conversation with Dawn and the young girl pretends to know nothing. Dawn asks questions about The Key and Glory reveals that The Key is very old then realizes Dawn knows nothing and is wasting her time. Dawn doesn't seem to remember exactly how Glory got into the room.
Buffy shows up in time to stop Glory from draining the energy from Dawn. With some help from the rest of the gang, Buffy gets in a few good hits and takes a few as well before Willow and Tara perform a spell to teleport Glory somewhere else. The godly one ends up high in the sky and falls straight to earth. Buffy shows Dawn that no matter what, they are sisters that are bound by blood.