The Stone Builders

Discord in Harmony
For the past decade, Humans and Wassarans have co-colonized the uninhabited planet of Ranklin. Despite giving their cities names like ‘Harmony’, not everyone is happy with the joint effort.
Human purists feel that anything not fully human is unnatural and should be cleansed.
Certain Wassaran sects feel the humans left their cradle/home planet far too early, and are not worthy of associating with their kind.
All this unrest simmers, unseen by most, until the accidental discovery of an underground city built eons ago by an unknown race. While scientists from both races try to understand this third culture, one of their Wassaran laborers is killed, and bombs are set off within the stone city.
Who built these underground cities? Where did they come from? And where did they go?
The answer could be worse than both the Purist and Wassaran fanatics. The same fate could await this colony, if someone doesn’t figure it out in time.