On The Darkest Nights

Is the large, multi-colored object Herbert Hull finds in Cemetery Woods near the base of Chimney Rock after it is split assunder by a massive lightning bolt really only another rock? He believes so, and hopes to sell it as a curiosity. However, the next morning he begins to have his doubts; it seems the object had grown slightly overnight and changed textures. Thus begins a string of unexplanable murders, all grissly and only on the darkest nights, that baffle the local sheriff's department.