"Wrong again," said Mr. Riddle. "I think you'll admit that I'm medium height for a man; but if I stood with my back to the door, my head wouldn't hit the top of the arch." "Nonsense. Let's see." Riddle took up the position indicated, facing them. "You're right!" ejaculated the young officer. "I'm amazed! I supposed it was much lower. What do you measure?" "Five feet eight inches. But it is the extreme width of the portal which makes it deceptive; it lowers it. I think, if I stretched out my arms, straight from the shoulder, I should no more than touch the side--see----" and he made a great cross of himself, against the black oak. "What are you fumbling at?" asked Kingsland sharply. "My fingers hardly touch--it's a stretch. Ah! now they do." "You look ghastly in the moonlight; put your arms down and come away." "I'm very comfortable here, barring my back; those silver nails are rather sharp," and he put his hands behind him. "Come away," said Kingsland, nervously, seeing something in his face he did not like. "You look as if you'd been walled up a few months ago, by some inquisition, and we'd just unearthed you in your niche." "By heavens! some of these nails are loose!" cried Riddle. "Nonsense!" retorted Kingsland. "You've thought so much about it, you'd imagine anything. They're as firm as--well, nails. I tried them myself. That door won't be opened in our lifetime, unless----" but the Lieutenant never finished his sentence, for he had paused suddenly, in open-mouthed astonishment. Without warning, and without a sound, the portal, closed for centuries, swung slowly inward, carrying Riddle with it; who, catching in vain at the sides of the door in an attempt to save himself, fell heavily backwards down three steps into the secret chamber. Seeing that he did not immediately rise, but turned over partially on his side, Kingsland recollecting himself, sprang forward to his aid, crying: "Have you hurt yourself?" "No, no," he replied, waving him off, and slowly rising from the floor, covered with dust. "By Jove!" exclaimed the Lieutenant. "How did you ever do it?" "Don't know, I'm sure," replied Riddle, emerging from the portal, and vigorously brushing himself. "As I told you, the nails, or some of them, felt loose--I pushed them, and the next thing I knew the door revolved and I was on the floor." "You're a genius!" exclaimed Kingsland. "But," peering down into the darkness of the tower, "where's Darcy's letter?" "We need a little light on the subject," said Mr. Riddle. Stepping to the fireplace, he lighted an old wrought-iron sconce, full of candles, which stood on the broad mantelshelf, and approached the secret door.