An ancient people built mystical fortresses made of melted stone; from the wall’s these fortresses defenders appeared to burn with a powerful energy and strike at their opponents with a supernatural force. Today most of these forts are abandoned and the art that made them lost.
Somehow, someway, a band of gnomes learns how to be ninjas. In fine gnomish style, they open an academy to teach this art to other gnomes. Wacky Hijinks ensue. Or the gnomes become some of the finest assassins in the land. Or both.