The Ninth Nightmare — Graham Masterton

When a thirteenth century monk was caught having a relationship with a married woman, his punishment was to have his arms and legs amputated. The Monk then turned against God and formed a sinister carnival of clowns and freaks, determined to corrupt everyone who saw them. However, when the pope goes after them, their only escape is into the world of the dreams. Eight hundred years later a serial killer finds a way to realize the carnival again. The Night Warriors are the world's only hope.