I stretched out a shaking hand and touched the surface of the slab. A faint thrill passed through my hand and arm, oddly unfamiliar and as oddly unpleasant; as of electric contact holding the very essence of cold. O’Keefe, watching, imitated my action. As his fingers rested on the stone his face filled with astonishment.

“It’s the door?” he asked. I nodded. There was a low whistle from him and he pointed up toward the top of the grey stone. I followed the gesture and saw, above the moon door and on each side of it, two gently curving bosses of rock, perhaps a foot in diameter.

“The moon door’s keys,” I said.

“It begins to look so,” answered Larry. “If we can find them,” he added.

“There’s nothing we can do till moonrise,” I replied. “And we’ve none too much time to prepare as it is. Come!”