A man tries to get into the library to see Giles, but a demon woman shows up and strangles him to death. He falls to the floor, and she turns into a puddle of green slime.
At school, we see Buffy and Willow playing 'Anywhere But Here' in which they recount their fantasies; Buffy is on a beach before sunset having her feet rubbed by Gavin Rossdale, Willow is in Florence at a restaurant eating ziti when she is joined by John Cusack. Giles tells Buffy to meet him later at the hospital where there will be a blood delivery, which attracts vampires. When Giles gets back to the library, a detective is waiting for him -- the dead man had Giles' address on him. Giles identifies the body as an old friend from London. The body has a tattoo on it, which Giles says he can't identify.
Shaken, Giles doesn't meet Buffy at the hospital, and she battles the doctor-dressed vampires alone until Angel shows up. She asks Angel to see to it that the blood gets to the hospital and goes to check on Giles. When Buffy goes to Giles' house to see what happened, he looks terribly drunk and sends her away. He calls another friend in London and finds out that she's dead, too. As he rolls up his sleeves, we see he has the same tattoo as his friend. Meanwhile, the dead friend, Phillip, comes back to life in the morgue, his eyes flashing, and escapes.
On Saturday, Willow, Xander, and Cordelia meet with Jenny Calendar -- Giles' girlfriend -- for a computer class. Buffy shows up to express her concern about Giles' behavior. Cordelia mentions the police visit to the library, which slipped her Cordelia-centered mind. In the library, Buffy finds Ethan, the costume shop owner and Giles' old friend who tried to kill her on Halloween. As she calls Giles, Ethan mentions the "Mark of Eyghon." Giles says she's in danger, and the dead Phillip enters.
A panicked Giles shows up and, after a scuffle which leaves Jenny unconscious, Phillip turns into the green goo. Some of it gets on Jenny and when she comes to, she seems normal but we see her eyes flash. Willow discovers the "Mark of Eyghon" in a book: Eyghon possesses the body of a dead or unconscious host. They figure out that he's jumped from Phillip's body to Jenny's. Possessed Jenny, looking and sounding like a demon, tries to seduce Giles at his apartment. When Buffy comes to the rescue, Jenny jumps out the window. Giles explains to Buffy that he ran with a bad crowd when he was young, and they used Eyghon as a temporary high -- directing him in and out of each others' bodies.
But one friend died, then later the girl who killed Phillip, and now it seems the rest of the group will die, too. Buffy goes to the deserted costume shop to try to help Ethan, but he knocks her out, ties her up and puts the mark of Eyghon on her. He then pours acid on his own tattoo so that Eyghon will take Buffy instead of him. Jenny enters, a complete demon, and Buffy breaks free. Angel enters suddenly and chokes Jenny: Eyghon's spirit leaves her body and enters Angel's, since he's really dead (Willow's plan). Eyghon fights Angel's demon, and is beaten. Jenny returns to normal, but Ethan escapes.