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!" A little later we were beside our boat.