"What is it?" asked Kent-Lauriston.
"I don't know."
"Let us examine."
"As far as I can make out, it's a flexible curtain of chain mail—hung across the staircase."
"I swear it moved," said the Lieutenant.
"No, it was the light which moved," replied the discoverer. "You see," and he swayed the sconce from side to side, making the curtain appear to be moving silently.
"If I take the light away," he continued, "there's nothing to be seen;" and he removed the sconce, leaving only the black mass of the steel curtain visible.
"Nothing to be seen—isn't there? Look there!" whispered Kingsland, and, following the direction of his eyes, the others saw a broad band of blood-red light steal out of the blackness, across the steps at the head of the staircase.
"That room has been closed for centuries, and yet there is a light burning," he continued hoarsely. "Shut the door, my dear fellow, and let's get away."
"It merely confirms another theory of mine," said Riddle, "which is, that, as there are no windows on the outside of the tower, they must have got their light and ventilation from the roof. I think it's fair to suppose that they used red glass, and that the full moon is shining through it."