The Green Pyramid

From the publisher's web site: You are brought to Yuggoth’s moon Thog, where you learn of the existence of the Zepzeg — a spacefaring alien species in many ways the antithesis of the Mi-Go. Plus, you learn of a lost colony of Gnorri here so far from your world. Can you reconcile the Zepzeg, the Gnorri, and your own goals? Negotiate with an antediluvian entity of enormous psychic power, assist the Gnorri and the Zepzeg to forge alliances to help you in the difficult strife ahead, and find the awesome grimoire detailing a weapon of unthinkable might.