A great disaster has befallen Hyboria. Somewhere on the Graskaal Mountains, the Heavenly Mountain fell, after which many peoples began to die under the blows of the Green Fire, also called Underground. The green fire did not leave anyone alive in its path; its destructive forces also affected Aquilonia. King Conan could not allow this to continue, having equipped a detachment of loyal people, Conan sets off to where the threat of the Green Fire comes from, to the mountains. In order to deal on the spot with what has fallen into a world alien to him.