Sentence:  This was the dream, that same damned recurrent dream, never "quite" the same dream — but on the same subject, night after night, chapter after chapter of the same story: as if he had bought a book of horror stories; they would all be on one theme, but told differently; that was the way with this string of <WSD>darkside</WSD> visions. 
Meaning of the word marked with <WSD> tags:  The side that is sad or distressing, metaphorically dark