And an ill day it was when first he darkened the threshold." Poirot waited for her indignation to subside, and then, resuming his business-like tone, he asked: "Now, as to this quarrel? 
The "he" that darkened the threshold is the master vampire.
mnli hypothesis: The "he" that darkened the threshold is the master vampire. premise: And an ill day it was when first he darkened the threshold." Poirot waited for her indignation to subside, and then, resuming his business-like tone, he asked: "Now, as to this quarrel? 