ere seemed no answer; and I was
compelled to give up the search for the moment, somewhat to the
amusement of Valguanera, who had watched curiously to see if I could
solve the mystery.

But I could not forget the subject, and towards noon started on another
tour of investigation. I procured the keys from the Cavaliere, and
examined the cells adjoining; they were apparently the same, each with
its window opposite the door, and nothing-- Stay, were they the same? I
hastened into the suspected cell; it was as I thought: this cell, being
on the corner, could have had two windows, yet only one was visible, and
that to the left, at right angles with the doorway. Was it imagination?
As I sounded the wall opposite the door, where the other window should
be, I fancied that the sound was a trifle less solid and dull. I was
becoming excited. I dashed back to the cell on the right, and, forcing
open the little window, thrust my head out.

It was found at last! In the smooth surface of the yellow wall was a
rough space, following approximately the shape of the other cell
windows, not plastered like the rest of the wall, but showing the shapes
of bricks through its thick coatings of whitewash. I turned with a gasp
of excitement and satisfaction: yes, the embrasure of the wall was deep
enough; what a wall it was!--four feet at least, and the opening of the
window reached to the floor, though the window itself was hardly three
feet square. I felt absolutely certain that the secret was solved, and
called the Cavaliere and Rendel, too excited to give them an explanation
of my theories.

They must have thought me mad when I suddenly began scraping away at the
solid wall in front of the door; but in a few minutes they understood
what I was about, for under the coatings of paint and plaster appeared
the original bricks; and as my architectural knowledge had led me
rightly, the space I had cleared was directly over a vertical joint
between firm, workmanlike masonry on one hand, and rough amateurish work
on the other, bricks laid anyway, and without order or science.

Rendel seized a pick, and was about to assail the rude wall, when I
stopped him.

"Let us be careful," I said; "who knows what we may find?" So we set to
work digging out the mortar around a brick at about the level of our
eyes.

How hard the mortar had become! But a brick yielded at last, and with
trembling fingers I detached it. Darkness within, yet beyond question
ther