through the air, without gaining knowledge of architectural
fundamentals; his mind, subconsciously, had been following strains and
stresses through those super-imposed curves. He turned abruptly to
Haldgren with a question.

"It seemed to me when I was following Anita that we climbed upward; we
were always running upward through the passages. We must be near the
surface of the Moon; is that true?"

Haldgren nodded slowly. "I think so--yes! In the great room out there
are windows of quartz high in the ceiling. You could not see them from
where you were, but they are there. I have seen them lighted; I think it
was the light of the sun."

"In that case," said Chet quietly, "I will ask you to open those doors."

"But they will come in!" the big man protested.

"They will not come in."

Chet turned to the girl. "I will ask you, my dear, to accompany me--if
you have faith."

And, to that, Anita Haldgren granted not even a word of reply. She moved
more swiftly than her brother to a controlling lever in the wall ... and
the ponderous doors swung slowly back.

* * * * *

Beyond those opening doors a din of shrieks went abruptly still. They
rose again in a squeaking babel of amazement and again were silenced as
Chet Bullard stepped through the arch. Beside him was the slender figure
of Anita; following was a stocky man whose unhandsome, face was alight
with a broad grin.

"Go to it, my bhoy!" Spud O'Malley was saying. "I don't know what you're
up to, but you'll be countin' me in--and here's hopin' you give those
devils hell!"

And, behind them all, in great strides that brought him up with the
rest, came Haldgren, recovered now from the stupefaction that had held
him momentarily. The four went silently where Chet led to the highest
point of the great terraced rostrum.

It was a stepped pyramid, Chet found, split in half and the half placed
against the wall. There was a stairway of smaller steps where priests,
some thousands of years before, had made their way to the top. And the
dust of centuries arose in smoky puffs as the four trod that path where
the holy ones had gone. Below them the silence was ending in sibilant
hissing calls as the black-winged beast-men watched that procession to
the heights. Some few had launched themselves into the air, Chet saw
when he turned.

"Tell them to go back," he said to Anita; "tell them to listen to what I
have to say!" There followed immediatel