A man, called Philip, turns up at Sunnydale High School looking for Giles. A security guard gives him directions to the library but before he can get there a demon woman show up and strangles him. He falls to the floor and she turns into a puddle of slime.

Outside the school, Giles tells Buffy to meet him later outside the hospital, because there is a blood delivery, which (surprisingly) attracts vampires. When Giles gets back to the Library he finds a detective waiting for him. Philip's body has been discovered and he had Giles's address on him. Giles identifies the body and tells the detective that Philip is an old chum of his from London. The body has an unusual tattoo on it, Giles says that he doesn't recognise it. Cordelia shows up after books and is surprised by Giles's shouting at her.

Giles doesn't go to the hospital so Buffy is left to fight the vampires on her own. They are dressed up as doctors (cute). Luckily Angel shows up and gives hera much needed hand. She asks Angel to make sure the hospital gets the blood and goes to find Giles.

She tracks him down at his apartment, very very drunk. He sends her away. he makes a phone call to London, to another old friend and finds out that she's dead too. After he hangs up, he rolls up his shirt sleeve to reveal a tattoo identical to the one on Philip's arm. While Giles is drowning his sorrows, Philip's corpse comes back to life in the morgue, eyes flashing and he escapes.

On Saturday, Xander, Cordy and Willow meet up with Jenny Calendar for computer class. Buffy show's up, worried about Giles's unusual behaviour. Xander -reminded of his Uncle Rory- asks if there were prostitutes present. When Buffy says no Xander relies with a there will be. Cordelia remembers the scene in the library and tells the others who can't believe that she didn't think it was important.

When Buffy and the others go to the Library, they find Ethan in there (the costume shop man) and she finds out that him and Giles are old old friends. When she demands to know what is going on, Ethan mentions the 'Mark of Eyghon'. Giles tells her that she is in danger and at that moment Philip (who's dead) walks in.

Giles panicks and there is a litle bit of a scuffle which ends up with Jenny lying unconscious on the floor next to the body of Philip. Philip starts to disolve into the slime, which inches across the floor and into Jenny. No one notices. When she comes around, she seems alright, but her eyes flash like Philip's.

Willow goes researching and discovers some information on the Mark of Eyghon. The demon Eyghon possesses the body of a dead (or unconscious) host. They figure out that he's jumped from Philip into Jenny's. Willow comes up with a plan to stop Eyghon once and for all, but she's going to need Angel's help.

While they are researching, Jenny, who even sounds like a demon is at Giles's apartment trying to seduce him. When Buffy comes to save Giles, jenny jumps out of the window. Giles tells Buffy that when he was younger he was part of a nasty crowd, into black magic and the like, and they used to summon Eyghon for fun.

But one of the group died when the possession went wrong, and now the group are being picked off one by one until only Ethan and Giles are left. Buffy goes to the costume shop to see Ethan, to offer help, which he repays by knocking her out and tying her face down to a table. When she comes around she finds Ethan tattooing the mark on her neck. When he's done, he pours acid over his own tattoo so when the demon tracks him down he'll take Buffy instead.

Jenny bursts in, a full demon with an icky face and everything. Buffy manages to break her bonds and fights Jenny. Angel somes in and takes over, throwing Jenny against the wall and choking her. The Demon leaves Jenny's body and goes into Angel's (part of Willow's cunning plan). Angel's demon is not pleased to be sharing and destroys Eyghon. Jenny collaspes and has to be helped out by Giles and Ethan does another runner, much to Buffy's annoyance.

The next day, Buffy is wearing a scarf to hide her new tattoo and is complaining that she's going to have to spend her entire allowance to get it removed before her mother notices. She says that the next time she has the misfortune to meet Ethan she's going to beat him until he bleeds.