Sentence:  When he reached the manse he went to his study and took down a bulky volume. ... He remained immersed in its mazes until dawn, struck a new trail of speculation and pursued it like a sleuth hound for the next week, utterly <WSD>lost to the world</WSD>, his parish and his family. 
Meaning of the word marked with <WSD> tags:  Mentally focussed on one's own thoughts or feelings, or on some task, to such a degree that one is unaware of other people or of one's surroundings; unconscious.