“That is quite true. But when, with their recent fixture, you couple the facts that they have been removed, that very careful measures have been taken to obliterate the traces of their presence, and that they would have been indispensable for the commission of the crime that we are almost certain was being committed here, it looks like an excess of caution to seek other explanations.”

“But,” I objected, “if the man, Graves, was really imprisoned, could not he have smashed the window and called for help?”

“The window looks out on the yard, as you see; but I expect it was secured too.”

He drew the massive, old-fashioned shutters out of their recess and closed them.

“Yes, here we are.” He pointed to four groups of screw-holes at the corners of the shutters, and, once more producing his lamp, narrowly examined the insides of the recesses into which the shutters folded.