'The Dark Age' Story Code '5V08' by Dean Batali and Rob Des Hotel

A man hurries nervously across the Sunnydale High campus at night, looking for Giles, but a decaying woman kills him, and as soon as his body hits the ground, she also collapses, dissolving into a puddle of blue-green goo. At Sunnydale High the next day, Ms Calendar arrives with a reminder of Saturday's computer tutorial for Willow and Xander, and romantic sparks fly between her and Giles. But they are interrupted by the arrival of police officers, who ask Giles to identify a body found outside the library. He identifies the man as Philip Henry, an old friend he hasn't spoken to in twenty years. Philip has a strange tattoo on his arm, which seems to disturb Giles, but he tells the police he doesn't know what it is. Concerned with his behaviour, Buffy goes to Giles' house, but he is curt and dismissive towards her. He calls a friend in England and discovers another old acquaintance, Deirdre Page, has recently died. On his arm, Giles has the same tattoo as Philip. That Saturday, Willow and Xander’s computer tutorial is interrupted before it begins by the arrival of Buffy, who reports Giles' odd behaviour. When Cordelia mentions Giles' meeting with the police, Buffy goes off to the library to call him; but when she arrives she is attacked by Ethan Rayne. She is able to overpower him and calls Giles, but the call is cut short when Philip's corpse walks through the library window. A fight breaks out, but Philip escapes, knocking Ms Calendar unconscious before being it too is rendered equally unconscious by Buffy. Philip then dissolves into a puddle of blue-green goo which seeps over Ms Calendar’s hand before she regains consciousness; she hugs Giles for comfort, but her eyes gleam strangely. Willow, Xander and Cordelia secretly research the mysterious ‘Mark of Eyghon’ that Ethan had mentioned. They discover that Eyghon is a demon that possesses an unconscious or dead host to live, but if the possession is not undone, it becomes permanent. After they realise that the demon must have possessed Ms Calendar, Buffy goes off to try to stop it. At Giles' home, Ms Calendar takes on a demonic visage and voice and attacks him; Buffy bursts in and drives her away, and Giles finally tells her his story: how, rebelling in his youth against the pressures of Oxford and his destiny as a Watcher, he fell in with a bad crowd and summoned Eyghon for the thrill of it. However, they lost control of the demon, and now Eyghon has returned to kill them all; only he and Ethan are left. Buffy goes to the costume shop to try to protect Ethan, but he knocks her unconscious; he tattoos her with the mark of Eyghon and uses sulphuric acid to remove his own. When the demonic ‘Ms Calendar’ shows up at the costume shop, she goes for Buffy, but the Slayer is able to break free and a fight ensues. After Giles arrives and demands that Eyghon take him instead, Willow and Xander appear with Angel, who attacks ‘Ms Calendar’. The demon leaps into the nearest dead host: Angel, but his inner demon fights and destroys Eyghon. Ethan disappears once again, while Ms Calendar finds herself haunted by the demon’s possession.

Sarah Michelle Gellar (Buffy Summers), Nicholas Brendon (Xander Harris), Alyson Hannigan (Willow Rosenberg), Charisma Carpenter (Cordelia Chase), David Boreanaz (Angel), Anthony Stewart Head (Rupert Giles), Robia LaMorte (Ms. Calendar), Robin Sachs (Ethan Rayne), Stuart McLean (Philip Henry), Wendy Way (Dierdre), Michael Earl Reid (Custodian), Daniel Henry Murray(Creepy Cult Guy), Carlease Burke (Detective Winslow), Tony Sears (Morgue Attendant), John Bellucci (Man)
Directed by Bruce Seth Green

TX (US): 10th November 1997
TX (UK - Sky One): 16th May 1998
TX (UK - BBC 2): 12th November 1999

Notes:
*Featuring Buffy, Xander, Willow, Giles, Cordelia and Angel