We climbed the first flight of stairs, and the duke turned sharp to the right.

We were now in a short corridor which ran north and south; three yards ahead of us was another turn, leading to the west wing of the house.

There was a window by us; the duke gently opened it; and over against us, across the base of the triangle formed by the building, was another window, four or five yards away.

The window was heavily curtained; no light could be seen through it.

But as we stood listening, the sounds began--first the gentle muffled hammering, then the sound of the file.