He has no servant with him.

He is all by himself at night.

Isn't it interesting?
A mystery in real life.

It baffles everybody." "You must be very strange people, my dear," I said, "to make a mystery of such a plain case as this." "Plain ?" repeated Lucilla, in amazement.
"Certainly! The gold and silver plates, and the strange tools, and the living in retirement, and the sending the servants away at night--all point to the same conclusion.

My guess is the right one.