This gave me an idea.
Carrying it back with me into the recess, I got down on my knees, and first taking the precaution to toss a little stick-pin of mine under the cabinet to be reached after in case I was detected there by Nixon, I insinuated the cutter between the base-board and the floor and found that I could not only push it in an inch or more before striking the brick, but run it quite freely around from one corner of the recess to the other.

This was surely surprising.

The exterior of this vestibule must be considerably larger than the interior would denote.

What occupied the space between?
I went upstairs full of thought.

Sometime, and that before long, I would have that cabinet removed..