While sitting around a camp fire the ponies decide to tell ghost stories to pass the time. Now it is Rarity's turn, and she recounts the events that happened to an old friend of hers, who happened to be an obtainer of antiques.
This was written as an inclusion to the campfire collaboration project, along with several other stories from other authors, each writing a spooky story using a different pony. However, the story itself is self contained.
This scared me.
Horrifying. Absolutely horrifying. The attention to detail, especially in describing Rarity's last encounter with Shiny Brass, is incredibly and horrifically well done.