With the first return of intelligence my mind gripped certain facts, and began to reason out the situation.

That sudden sweep of air could only have originated in the opening of some other barrier--a door no doubt leading directly to the outside.

I had seen no occupant of the room; without question it was deserted at my entrance.

Yet someone had been there, and not long before, as was evidenced by the burning candle.

Nor, by that same token, did this same mysterious party expect to be absent for any length of time.
Apparently I had intruded at the very moment of his departure.
Wherever that second passage might be, the former occupant of this underground den had evidently entered it previous to my opening the inner door.