The Restless Door was created in an unknown hell dimension.
The Restless Door was first shown used by Archaeus, who released a Morituri demon from its dimension to attack the Scooby Gang. They then tracked the artifact and found him in San Francisco's shipyard, within multiple layers of magical protection, which broke Xander's favorite axe in an attempt to destroy it. Willow was able to reduce its protection into two layers, so Buffy attacked the Restless Door with her scythe, breaking it in three pieces.
The fragments, though, were stolen by the Mistress, Soul Glutton, and Sculptor, who restored the artifact. In their power, they attempted to fill the Earth with creatures who owe them a debt for making the journey possible. It first released a demon that targeted Xander and Giles, but was killed by Willow. In a world-wide scale, it released a giant horned gorilla demon in Buenos Aires, ice demons in Ontario, flying centipedes in Italy, among others, caused thousands of deaths, despite the assistance of the second formation of the Magic Council and Deepscan as military contractors. With the government intervention, Willow helped put down four demon invasions in a week, but they weren't on time for "a snake the size of a subway train" when sixteen people were eaten alive; the next week, they defeated a group flying brain demons in Montana, avoiding a massacre. Buffy, Spike, Willow, and the Magic Council fought a Kraken in the Hoover Dam, sending it back to its dimension. With the death of the Sculptor, the Mistress and the Soul Glutton became the solo users of the Restless Door.
While the Council was repelling an intermensional invasion from the Hell of Screams, the Scoobies found the Restless Door and its users in the Black Diamond Mines. The Mistress and the Soul Glutton avoided their defeat by opening a portal to Anharra and destroying the Restless Door. The artifact was irrevocably shattered, but its absence resulted in an impending apocalypse: the portal would remain expanding until both worlds were joined. Fortunately, the Scoobies crossed the portal to its original dimension, where Dawn was able to use her key powers and close the portal.
The Restless Door was a small chest with purple crystals, with a key-like winged golden object inside it.
- Old Demons, Part One (Only mentioned)
- Old Demons, Part Two
- Old Demons, Part Three
- In Pieces on the Ground, Part One (Only mentioned)
- In Pieces on the Ground, Part Four
- In Pieces on the Ground, Part Five (Only mentioned)