Sentence:  Neither were they connected with fear: he was conscious of no fear. Rather, they originated in a strange <WSD>besetting</WSD> desire to know what to do when the time came; a desire gigantically disproportionate to the few swift moments to which it referred; a wondering that was more like the wondering of some other spirit within his, than his own. 
Meaning of the word marked with <WSD> tags:  Obsessive