"I will go alone," said T. B., and Fall, with a little bow, closed the gates, and the lift descended.
They waited some time; Fall had the power, from where he was, of closing the gates below and bringing the lift up again. This Poltavo knew to his cost, but there were good reasons why the doctor should not exercise his knowledge, and in a few minutes the lift came back to its original position and T. B. stepped out.
"Thank you, I have learned all I want to know," he said with a keen glance at Poltavo. "Really, you have an extraordinary house, Dr. Fall."
"It is always open to your inspection," said the doctor, with a heavy smile.
T. B. was fingering the little electric lamp, which he carried in his hand, in an absent-minded manner. Presently he put it into his pocket, and, with a nod to his host, walked across the hall. He turned suddenly and addressed Poltavo.
"When you were trapped in this house," he said, quietly, "and expected considerable trouble in escaping from the trap, you took the precaution, like the careful man that you are, of inscribing a message which might aid those who came to your relief. This message has now served its purpose," he smiled, as he saw the look of consternation on Poltavo's face, "and you will be well advised to invite your friend to wipe it out"; and with another nod he passed from the house, followed by his three men.
"What does this mean?" asked Fall, quickly.
"I—I—" stammered Poltavo, flustered for once in his life, "wrote on the side of the lift a few words only, nothing incriminating, my dear doctor, just a line to say that I was imprisoned below."
With a curse Fall dashed into the little elevator.
"Bring a light," he said, and struck a match to read the scrawl which Poltavo had written. Fortunately there was nothing in it which betrayed the great secret of the house, but it was enough, as he realized, to awaken the dormant suspicion, even supposing it was dormant, of this indefatigable detective.