importance to identify the house, and it is your duty to secure the
means of doing so."

"But, my dear Thorndyke," I expostulated, "I have told you how I was
conveyed to the house. Now, will you kindly explain to me how a man,
boxed up in a pitch-dark carriage, is going to identify any place to
which he may be carried?"

"The problem doesn't appear to me to present any serious difficulties,"
he replied.

"Doesn't it?" said I. "To me it looks like a pretty solid impossibility.
But what do you suggest? Should I break out of the house and run away up
the street? Or should I bore a hole through the shutter of the carriage
and peep out?"

Thorndyke smiled indulgently. "The methods proposed by my learned friend
display a certain crudity inappropriate to the character of a man of
science; to say nothing of the disadvantage of letting the enemy into
our counsels. No, no, Jervis; we can do something better than that.
Just excuse me for a minute while I run up to the laboratory."

He hurried away to Polton's sanctum on the upper floor, leaving me to
speculate on the method by which he proposed that a man should be
enabled, as Sam Weller would express it, "to see through a flight of
stairs and a deal door"; or, what was equally opaque, the wooden
shutters of a closed carriage.

"Now," he said, when he returned a couple of minutes later with a small,
paper-covered notebook in his hand, "I have set Polton to work on a