He moved back, so that the weight of his body bore upon the rear instead of the fore end of the stone. Then, however, he found that he could not reach the hand-grip.
"Why not try the other side?" said Warrender. "There may be another grip there."
The other side of the staircase was open to the cellar, and Armstrong was able to thrust his arm into the aperture below the step without treading on the flagstone.
"Got it!" he said, a moment later. "There's a grip here. It moves in a quarter-circle. Something--a disk of stone, I fancy--is revolving."
He pressed on the flagstone; still there was no distinct movement downwards, though it seemed to have yielded a trifle.
"Clearly it won't shift until the other grip is turned," he said. "But how to get at that?"
After a little consideration he had another idea. Going a few steps up the staircase, he turned, and crawled down head first until he was able to get his hand under the edge of the stone.
"All right, old man," he said, cheerfully. "I've moved the grip now. Keep clear of the other end of the stone."
Lying full stretch on the staircase, he pressed on the stone beneath him. It sank gently; the other end moved upwards, and in a few seconds the stone stood upright in the middle of a dark gap. Warrender bent down, holding the electric torch just above the opening.
"The bottom's only about five feet deep," he said. "It's the end of some sort of passage. Come down, old man, and we'll explore it together."