The thinner air of Mars scarcely softened them, but left them hard and gem-bright. There was no moon, of course, not one such as Earth knew. Mars's two satellites, Phobos and Deimos, were tiny things only five or ten miles across, simply mountains flying loose in space. Even though they were much closer to Mars than the Moon was to Earth, they would show no disk and be only two more stars.

He searched for them, even though he realized they might easily both be on the other side of Mars. Low on the western horizon he caught something else. Slowly he turned to it. It was by far the brightest object in the sky, with a faint blue-green tinge to it that was matched for beauty by nothing else in the heavens he watched. Separated from it by about the width of Mars's shrunken sun was another object, yellower, bright in itself but dwarfed by the much greater brillance of its neighbor.

David needed no star map to identify the double object. They were the Earth and the Moon, the double "evening star" of Mars.

He tore his eyes away, turned toward the low outcropping of rock visible in the light of his pencil flash, and began walking. Bigman had told him to use those rocks as a guide. It was cold in the Martian night, and David was regretfully aware of the heating powers of even the Martian sun, one hundred and thirty million miles away.

The sand-car was invisible, or nearly so, in the weak starlight, and he heard the low, even purr of its engines long before he saw it.

He called, "Bigman!" and the little fellow popped out of it.

"Space!" said Bigman. "I was beginning to think you were lost."

"Why is the engine running?"

"That's easy. How else do I keep from freezing to death? We won't be heard, though. I know this place."

"Do you have the films?"

"Do I? Listen, I don't know what you had in the message you sent but they had five or six scholars circling me like satellites. It was 'Mr. Jones this' and "Mr. Jones that.' I said, 'My name's Bigman,' I said. And then it was 'Mr. Bigman, if you please.' Anyway"-Bigman ticked items off on his fingers-"before the day was gone, they had four films for me, two viewers, a box as big as myself which I haven't opened, and the loan (or maybe the gift for all I know) of a sand-car to carry it all in."

David smiled but made no answer. He entered Into the welcome warmth of the car and quickly, in a race to outrun the fleet night, adjusted the viewers for projection and inserted a film in each. Direct viewing would have been quicker, more preferable, but even in the warm interior of the sand-car his nosepiece was still a necessity, and the bulbous transparent covering of his eyes made direct viewing impossible.

Slowly the sand-car lurched forward through the night, repeating almost exactly the route of Griswold's subsection on the day of the checkup.

"I don't get it," said Bigman. He had been muttering under his breath uselessly for fifteen minutes and now he had to repeat his louder statement twice before the brooding David would respond.

"Don't get what?"

"What you're doing. Where you're going. I figure this is my business because I'm going to stay with you from here on. I've been thinking today, Mr. St- Williams, thinking a lot. Mr. Makian's been in a kind of biting temper for months now, and he wasn't a bad joe at all before that. Hermes came in at that time, with a new shuffle for all hands. And Schoolboy Benson gets his licks in all of a sudden. Before it all started he was nobody, and now he's real pally with the big shots. Then, to top it off, you're here, with the Council of Science ready to put up anything you want. It's something big, I know, and I want to be in on it"

"Do you?" said David. "Did you see the maps I was viewing?"

"Sure. Just old maps of Mars. I've seen them a million times."

"How about the ones with the crosshatched areas? Do you know what those areas stood for?"

"Any farmboy can tell you that. There are supposed to be caverns underneath, except that I don't believe it. My point is this. How in Space can anyone tell there are holes two miles underneath the ground if no one's been down there to see? Tell me that."

David did not bother to describe the science of seismography to Bigman. Instead, he said, "Ever hear of Martians?" Bigman began, "Sure. What kind of a question____________________ " and then the sand-car screeched and trembled as the little fellow's hands moved convulsively on the wheels. "You mean real Martians? Mars Martians; not people Martians Eke us? Martians living here before people came?"

His thin laugh rattled piercingly inside the car and when he caught his breath again (it is difficult to laugh and breathe at the same time with a nosepiece on), he said, "You've been talking to that guy Benson."

David remained gravely unruffled at the other's glee. "Why do you say that, Bigman?"

"We once caught him reading some kind of book about it, and we ribbed the pants off him. Jumping Asteroids, he got sore. He called us all ignorant peasants, and I looked up the word in the dictionary and told the boys what it meant. There was talk of mayhem for a while, and he got shoved around sort of by accident, if you know what I mean, for a while after that. He never mentioned anything about Martians to ms after that; wouldn't have had the nerve. I guess, though, he figured you were an Earthman and would fall for that kind of comet gas."

"Are you sure it's comet gas?"

"Sure. What else can it be? People have been on Mars for hundreds and hundreds of years. No one's ever seen Martians."

"Suppose they're down in the caverns two miles underneath."

"No one's seen the caverns either. Besides, how would the Martians get there in the first place? People have been over every inch of Mars and there sure aren't staircases going down anywhere. Or elevators, either."

"Are you certain? I saw one the other day."

"What?" Bigman looked back over his shoulder. He said, "Kidding me?"

"It wasn't a staircase, but it was a hole. And it was at least two miles deep."

"Oh, you mean the fissure. Nuts, that doesn't mean anything. Mars if full of fissures."

"Exactly, Bigman. And I've got detailed maps of the fissures on Mars too. Right here. There's a funny thing about them which, as nearly as I can tell from the geography you brought me, hasn't been noticed before. Not a single fissure crosses a single cavern."

"What does that prove?"

"It makes sense. If you were building airtight caverns, would you want a hole in the roof? And there's another coincidence. Each fissure cuts close to a cavern, but without ever touching, as though the Martians used them as points of entrance into the caverns they were building."

The sand-car stopped suddenly. In the dim light of the viewers, which were still focused on two maps projected simultaneously upon the flat white surface of the built-in screens, Bigman's face blinked somberly at David in the back seat.

He said, "Wait a minute. Wait a jumping minute. Where are we going?"

"To the fissure, Bigman, About two miles past the place where Griswold went over. That's where it gets nearest the cavern under the Makian farms."

"And once we get there?"

David said calmly, "Once we get there, why, I'll climb down into it."