A stone sacred to the dwarven people, believed to be one of eight divine relics somehow central to the integrity of reality itself.
Legend says it was forged by Moradin, god of dwarves, and used to fuel the fire at the heart of the Great Mountain.
Two months ago, it was in the SPI’s possession. They were studying it. Then the SPI exploded in flames one night—it may or may not have been the Stone which was responsible… afterward, the Arkenstone was gone.
The SPI agents have since realized that the stone was reclaimed by Moradin; given to Hyperion, the Titan of Ice; embedded into the pommel of a sword; and gifted to Hyperion’s adopted son Callisto prior to sending him out into the world to purge the world of the undead scourge.