From the Back of the Book:
Unknown to even the mightiest of the great sorcerer-kings, a fire is stirring deep beneath the barren soil of Athas. Sheltered by the titanic bulk of the Black Spine mountains, a terrible force has ripped open the very fabric of time and space. Now a shimmering portal stands open and a long-forgotten enemy assembles its sinister forces to invade the kingdoms under the dark sun.
The only thing that stands in the way of that terrible fate is a band of heroes. Assembled from the four corners of this tortured world and bound together by the tangled cords of fate, they must face an enemy the likes of which they have never seen before. The odds are against them, but they dare not fail. The fate of the world is in their hands.
Black Spine is an adventure for 4 to 6 characters of 10th through 13th level. The previous flip-book modules (Black Flames, Merchant House of Amketch, and Marauders of Nibenay) precede this adventure, but they are not necessary to enjoy Black Spine.