"We have left the door ajar."
"Still I think you will find a difficulty in getting out," insisted the other. "Open the door."
Ela pulled at it, but it was impossible to move the heavy oaken panel.
"Electrically controlled," said the doctor; "and you can neither move it one way nor the other. It is an ingenious idea of mine, for which I may also apply for a patent one of these days."
He took a key from his pocket and inserted it in an almost invisible hole in the oak panelling of the hall; instantly the door opened slowly.
"I wish you a very good night," said Doctor Fall, as they stood on the steps. "I hope we shall meet again."
"You may be sure," said T. B. Smith, grimly, "that we shall."