Russell Clyde was confined to his bunk during the next four days, his feet wrapped in bandages and ointment. Fortunately the digestive juices of the Venusian amoeba had only just begun their attack upon the skin after eating through the footgear. Except for some painful blisters and rawness, his condition was not serious.

The little stateroom was cramped, containing as it did two bunks, one above the other, like the cabin of a liner. What with a couple of built-in lockers for clothes, and a bolted-down chair and a reading lamp, it was not a place to spend any more time than necessary. The lack of a window added to the inhospitality of the room. But Burl had accepted long ago the fact that a spaceship could not yet be considered a luxury liner. In time, the A-G drive would permit such things, but the Magellan was an experimental vessel turned by emergency into a warship.

During those four days, Burl spent most of his time with Russ, getting to know him better, and talking about the trip. The young astronomer was not at all chagrined by his misadventure. In fact, the whole experience had him quite buoyed up.

"What a wonderful place for biologists to study! Venus will be a Mecca for scientific learning!"

"But not for anything else, I don't think," said Burl. "Anyway, we're in for another experience now. Mars is our next goal. What's it like?"

Russ put his hands behind his head and looked up at the bottom of the bunk above him. "We can see Mars well enough; there's no cloud blanket and the atmosphere is thin but clear. You've seen the photos and the colored sketches?"

"I've seen it from our viewplates, but so far it's just a tiny, red disc. We're about at Earth's orbit now, even though Earth is many millions of miles away from us. Mars is still about fifty million miles further, but we're gaining speed quite rapidly and Lockhart thinks we'll make it soon enough." Burl picked up one of the books from the ship's library and started to thumb through it to locate a color chart of the planet.

Russ waved a hand. "You don't have to show me. I've studied Mars by telescope so often I know it by heart. It's mostly a sort of light, reddish-tan, a kind of pale russet. We think that's desert. There are some fairly large sections that are bluish-green—at least in the Martian summers. In their winters these sections fade very greatly."

"That's vegetation," Burl broke in. "It must be! Everybody agrees it acts like it. And there are the white polar caps, too."

"You can tell which season is which by the size of the polar ice caps. When one is big, the other is almost gone. Then there's the problem of the canals...."

"Do you believe in them?" asked Burl. "The books disagree. Some think they're real—even say they look as if they had been built by intelligent beings as irrigation channels to take the melting waters of the poles down to the fertile lands. But other astronomers claim they can't see them—or that they're illusions, series of cracks, or lines of dark dust blown by winds."

"Personally, I've come to believe in them," Russ argued. "They've been photographed—something is there. They're very faint, spidery lines, but they certainly are straight and regular. We'll find out soon enough."

Find out they did. Russ was up and about and the normal life of the ship resumed. During their passage of Earth's orbit, they had managed to raise the United States on the ship's radio. For three days they were able to converse with their home base. They exchanged news and data, transmitted back all they had learned and eagerly asked for news.

The men of the crew had the chance to send messages home, and Burl even talked briefly with his father. There had been an important discovery made on Earth.

The lines of force had finally been traced. The distortions visible on Mars, as well as the one from Mercury before its cutoff, had been worked out directionally. There was no doubt that a line of force had been channeled outward to a point in space that now proved to be that of a planet. The planet was Pluto.

"Pluto!" That was the shocked word uttered by everyone within hearing distance when the radio voice said it.

"Pluto! Why, that's the end of the line! The most distant planet," said Oberfield, shocked. "We'll have to go there—all the way!"

That fact sobered everyone. It meant the trip must last many times longer than anyone had expected. But they were a band of men who had achieved great things—they had managed so far to work together in harmony, and they felt that since they had conquered two planets—what were a few more?

Mars gradually grew larger on their telescopic viewers as the Magellan fell onward through space, riding the beam of gravity that was like a pulling rope to them. The slow down and reverse was made in good order—the sphere swinging around, readjusting, and the great, driving Zeta-ring generators now pushing and braking.

Then one wake period, Russ and Burl went to the telescope and trained it again on the oncoming planet. The now large disc of the ruddy world swung onto the screen. It looked strange, not at all like the drawings.

Burl had never seen it through Terrestrial telescopes, but he sensed something was wrong. He realized suddenly, "Both poles are enlarged! It's winter on both hemispheres! And that's impossible!"

Yet it was so. Both the Martian ice caps were present and both extended down the northern and southern hemispheres of the world. The men stared in silence.

Slowly Russ tried to figure it out, "The greenish-blue areas can scarcely be seen. Where they should be, there're darker patches of brown, against the yellowish-red that now seems to be the desert areas. It seems to be winter on both sides and it looks bad. It looks to me as if Mars were a fast-dying world."

Burl squinted his eyes. "Yet I see the canals. The straight lines are still visible—see?"

Russ nodded. "They're real. But what's happened?"

Indeed, the planet seemed blighted. "It's the Sun-tap," Burl decided. "We should have realized what it would do."

"Remember Earth the week it was working? The temperature fell several degrees, began to damage crops? Remember how it snowed in places where snow had never fallen in July? Remember the predictions of disaster for crops, of danger from winter snows if the drop continued?"

Russ went on in his careful, explanatory way. "And for Mars it has continued. Mars was always colder than Earth; life there must have been far more precariously balanced. During the day, on the Martian equator in midsummer, the highest temperature is not likely to be more than 70° or 80°; and at night, even then, it would fall below freezing. Vegetation on Mars must have been hardy in the best of times, and life carried on under great difficulties.

"Now the margin of warmth and light has been cut. It has been just enough to keep both polar caps frozen, to prevent water from reaching the fertile regions, and the cold has advanced enough to bar the growth and regeneration of plant life. If the Sun-tapping on Mars is not stopped, all life there will die out, and it will be a permanently dead world forever."

The news spread throughout the crew and there was a feeling of anger and urgency. Nobody knew what lived on Mars, yet the subject of Mars and Martians had always intrigued the imaginations of people on Earth. Now, to hear that the unknown enemy had nearly slain a neighboring world brought home vividly just what would also have been the fate of Earth.

The day finally came when the big spaceship slid into an orbit about the ruddy planet. It circled just outside the atmospheric level while the men aboard studied the surface for its secrets.

Mars was indeed inhabited. This fact was borne home by the canals and the very evident artificial nature of their construction. They could see clearly through their telescopes that there was an intricate global network of pipelines, pumping stations, and irrigation viaducts from pole to pole. They also saw that at the intersections of the canals were dark sections crisscrossed with thin blobs of gray and black which proved under the telescopes to be clusters of buildings. There were cities on Mars, linked by the waterways.

They saw no aircraft. They detected no railroad lines or roadways beyond the canalways themselves. The many regions of darker, better ground, intersected by the canals which no longer fulfilled their purposes, were covered with thick vegetation—forests of dying, wintery stalks. Only a flicker of dark green here and there showed where some faint irrigation still got through.

They saw also that there were lines of white, which had not been visible before. Snow was gathering in low spots, and the planet was freezing up.

The lines of solar distortion were strong, and they traced them to their point of concentration. The point was not some isolated spot far in a desert, away from Martian investigation. To the amazement of the men, the location of the Sun-tap station was actually within a Martian city!

"Do you suppose," Lockhart queried the others, "that the Martians themselves are the builders of this setup—that this is their project—that they are the criminals and not the victims?"

There was no answer. The evidence was apparent, but it made no sense. If the Martians had created this thing, it was destroying them. And yet, if they had not created it, why did they—so clearly a race that had attained a high level of engineering ability—tolerate its continual existence?

As the ship descended, they saw the city emerge. It consisted of hundreds of gray mounds—buildings laid out in the form of neat hemispherical structures, like skyscraper igloos, with rows of circular windows. Each building was like the next, and they fitted together in a series of great circles, radiating outward from the meeting spot of the canals.

The explorer crew waited at the ship's rocket launchers for an attack. The tail of the teardrop housed the built-in armament—the rocket tubes which could send forth destruction to an enemy. But though Haines sat with his finger on the launcher button, no aircraft rose to meet them from the city below. No guns barked at them. No panic started in the streets.

They could see tiny dots of living beings moving about, but no sign of alarm, no evidence that they had been noticed.

Even here, at the equator, there were streaks of white snow in the streets and rings of rime along the bases of the buildings.

Directly below them lay the Sun-tap station. The lines converged here, and the rings of distortion could be seen in the atmosphere, causing the city to flicker as if from the presence of invisible waves.

Then they saw the masts and their shining accumulators projecting about a cleared spot near the outskirts of the city. The customary walled ring and the open machinery were not visible.

"The Sun-tap station is under the city!" said Lockhart, shocked. "It's been built beneath the streets somewhere, and the Martians walk around above it and let the masts alone! They must be the builders!"

"If so, why are they killing themselves?" Burl couldn't see the sense of it. "And if they have reasons, then why don't they defend it? They were alerted while we were on Mercury. They must have spaceships if they are the enemy. Where are they?"

The ground was now but a few hundred feet below them, and still no one paid the strange ship hanging in the sky any attention. While the crew stood with bated breath, Lockhart brought the ship down and down, until it came to rest barely fifty feet above an intersection. There it hung, nearly touching the roofs, and was ignored.

The shining masts of the Sun-tap station continued to gleam, following the tiny bright Sun in its course through the dark blue of the sky. One of the two small Martian moons was climbing upward along the horizon. The canals beyond were dark lines of conduit, through which no life-giving waters flowed. And the Martians did nothing.