The indefinite word in this sentence is "all'' because it is formed from a indefinite pronoun therefore it is a indefinite adjective.
a)He believes it is stealthy and all-encompassing.
He describes the fog as being everywhere when he says its on the window-panes, in the drain pools, and "into the corners of the evening". All-encompassing means that it is everywhere, surrounding everything. The way the speaker leaves out any mention of sound or noise makes it seem as though this fog moves quietly. The description of the fog going to the window-panes, the corners, and the pools gives it a quick stealthy feel.
