While Rarity goes on a gem hunt by herself, she stumbles across an unusual gem. This gem seems to glow a faint red and pink color.. She has never seen such a gem before and it intrigues her. She decides to take it back to the shop and maybe put it on a dress or a necklace just for her.

But soon, the mares of Ponyville begin to act strange. What's happening to them, and why does it seem to revolve around this gem she wears around her neck?