“They use none. There is a stove. The bell-rope hangs from the wire just to the right of my desk. Whoever rang it must have come right up to the desk to do it. But why should any criminal wish to ring the bell? It is a most insoluble mystery.”

“Certainly the incident was unusual. What were your next steps? You examined the room, I presume, to see if the intruder had left any traces⁠—any cigar-end or dropped glove or hairpin or other trifle?”

“There was nothing of the sort.”

“No smell?”

“Well, we never thought of that.”

“Ah, a scent of tobacco would have been worth a great deal to us in such an investigation.”