"I guess we're getting jumpy," Paul whispered nervously, his breath steaming in the cold, frosty air that filled the shelter.
"It looks that way," Evan Harwich returned reassuringly.
But after the boy was asleep again, he crept back to the frosted window to watch. He knew that there had to be something mighty on Io. The shell of force that surrounded the evil moon couldn't exist all alone. There had to be more. Something that lay back of it, went with it. Something that could easily be very dangerous.
Jupiter, so near to Io, was a gigantic threatening mass in the heavens. But its light was deceptive. There were so many dense shadows.
Did he see some of the stars near the horizon wink out suddenly, and then appear again, as though something big and nameless and sinister had momentarily blocked their light and then passed on? He could not be sure, and nothing further happened. To save his companion unnecessary concern, when nothing could be done about the threatening danger anyway, he decided to keep the incident to himself.
Long before the dawn they were once more on the march. How many hours was the Ionian day? Something over forty. It didn't matter much.
When the daylight finally came, they had slept again, this time in their space suits, without bothering to set up the tent. Rising to his feet, Paul Arnold pointed suddenly.
"Look! An ancient road!" he shouted.
It was true. The highway ran there between the hills. A stone ribbon, covered here and there with drifted sand, which showed that there was no traffic of any sort now. The ruins along it looked a little less battered than those which the two men had previously seen, and there were vast lumps of corroded metal, too. Machinery in a former age.