The Keep — F. Paul Wilson

The message is received from a Nazi commander stationed in a remote castle high in the Transylvanian alps:

"Something is murdering my men."

Immediately an elite SS extermination squad is sent to destroy whatever enemy dares challenge the might of the Third Reich. And the battle is joined. A battle more awesomely terrifying than anything ever experienced. Between the ultimate evil created by man... and the unthinkable, undreamed of, undead horror it has awakened from centuries of darkness to suck the life from living souls again.