From back cover: "You are the Wizard Grey Star. Your quest is to retrieve the legendary Moonstone and with its power throw down the evil Wytch-king. You must find the Shadow Gate—doorway to the magic realm where it lies hidden. When the moon is full, the Shadow Gate appears—in Desolation Valley beyond the Mountains of Morn, where you must dare The Forbidden City. The Wytch-king will try to track you down. His slaves will dog your every step—the cruel warriors of Shadaki, the phantom spirit of the Deathgaunt and the dark horror of the demon Kleasá. Only your Magical Powers and the might of your Wizard's Staff can protect you in a terrifying adventure of madness, magic and menace!"
The book is the second installment in the series The World of Lone Wolf, which is a derivate of the Lone Wolf series.