"You can't do it. But I'll make you a deal if you want. It's eleven now. Give me two of your 0-tanks, and we'll go back to town. We'll stop two hours from town, leave your buggy; and you'll ride the rest of the way tied up in the air bin. Then you can stand trial."

"You think they'll let me off?"

"Not after the way you ripped the bubble open on your way out. That was a blunder, Jack."

"Why don't you just take one tank?" If Alf did that, Carter would get back with two hours to spare. He knew, now, that he would have to wreck the bubble. He had no alternative. But Alf would be right behind him with the flare gun...

"No deal. I wouldn't feel safe if I didn't know you'd run out of air two hours before we got back. You want me to feel safe, don't you?"

It was better the other way. Let Alf turn back in an hour. Let Alf be in the bubble when Carter returned to tear it open.

"Carter turned him down," said Timmy. He hunched over the radio, holding his earphones with both hands, listening with every nerve for voices which had almost died into the distance.

"He's planning something," Gondot said uneasily.

"Naturally," said Shute. "He wants to lose Alf, return to the bubble, and wreck it. What other hope has he?"

"But he'd die too," said Timmy.

"Not necessarily. If he killed us all, he could mend the new rip while he lived on the O-tanks we've got left. I think he could keep the bubble in good enough repair to keep one man alive."

"My Lord! What can we do?"

"Relax, Timmy. It's simple math." It was easy for Lieutenant-Major Shute to keep his voice light, and he didn't want Timmy to start a panic. "If Alf turns back at noon, Carter can't get here before noon tomorrow. At four he'll be out of air. We'll just keep everyone in suits for four hours." Privately he wondered if twelve men could repair even a small rip before they used up the bottled air. It would be one tank every twenty minutes... but perhaps they wouldn't be tested.

"Five minutes of twelve," said Carter. "Turn back, Alf. You'll only get home with ten minutes to spare."

The linguist chuckled. A quarter mile behind, the blue dot of his buggy didn't move.

"You can't fight mathematics, Alf. Turn back."

"Too late."

"In five minutes it will be."

"I started this trip short of an O-tank. I should have turned two hours ago."

Carter had to wet his lips from the water nipple before he answered. "You're lying. Will you stop bugging me? Stop it!"

Alf laughed. "Watch me turn back."

His buggy came on.

It was noon, and the chase would not end. At twenty-five miles per, two Marsbuggies a quarter of a mile apart moved serenely through an orange desert. Chemical stains of green rose ahead and fell behind. Crescent dunes drifted by, as regular as waves on an ocean. The ghostly path of a meteorite touched the northern horizon in a momentary white flash. The hills were higher now, humps of smooth rock like animals sleeping beyond the horizon. The sun burned small and bright in a sky reddened by nitrogen dioxide and, near the horizon, blackened by its thinness to the color of bloody India ink.

Had the chase really started at noon? Exactly noon? But it was twelve-thirty now, and he was sure that was too late.

Alf had doomed himself-to doom Carter.

But he wouldn't.

"Great minds think alike," he told the radio.

"Really?" Alf's tone said he couldn't have cared less.

"You took an extra tank. Just like me."

"No I didn't, Jack."

"You must have. If there's one thing I'm sure of in life, it's that you are not the type to kill yourself. All right, Alf, I quit. Let's go back."

"Let's not."

"We'd have three hours to chase that Martian."

A flare exploded behind his buggy. Carter sighed raggedly. At two o'clock both buggies would turn back to bubbletown, where Carter would probably be executed.

But suppose I turn back now?

That's easy. Al f will shoot me with the flare gun.

He might miss. I f I let him choose my course, I'll die for certain.

Carter sweated and cursed himself, but he couldn't do it. He couldn't deliberately turn into Alf's gun.

At two o'clock the base of the range came over the horizon. The hills were incredibly clear, almost as clear as they would have been on the moon. But they were horribly weathered, and the sea of sand lapped around them as if eager to finish them off, to drag them down.

Carter rode with his eyes turned behind. His watch hands moved on, minute to minute, and Carter watched in disbelief as Alf s vehicle continued to follow. As the time approached and reached two-thirty, Carter's disbelief faded. It didn't matter, now, how much oxygen Alf had. They had passed Carter's turnover point.

"You've killed me," he said.

No answer.

"I killed Lew in a fistfight. What you've done to me is much worse. You're killing me by slow torture. You're a demon, Alf."

"Fistfight my aunt's purple asterisk. You hit Lew in the throat and watched him drown in his own blood. Don't tell me you didn't know what you were doing. Everybody in town knows you know karate."

"He died in minutes. I'll need a whole day!"

"You don't like that? Turn around and rush my gun. It's right here waiting."

"We could get back to the crater in time to search for that Martian. That's why I came to Mars. To learn what's here. So did you, Alf Come on, let's turn back."

"You first."

But he couldn't. He couldn't. Karate can defeat any hand-to-hand weapon but a quarterstaff, and Carter had quarterstaff training too. But he couldn't charge a flare gun! Not even if Alf meant to turn back. And Alf didn't.

A faint whine vibrated through the bubble. The sandstorm was at the height of its fury, which made it about as dangerous as an enraged caterpillar. At worst it was an annoyance. The shrill, barely audible whine could get on one's nerves, and the darkness made streetlamps necessary. Tomorrow the bubble would be covered a tenth of an inch deep in fine, moon-dry silt. Inside the bubble it would be darker than night until someone blew the silt away with an O-tank.

To Shute the storm was depressing. Here on Mars was Lieutenant-Major Shute, Boy Hero, facing terrifying dangers on the frontiers of human exploration! A sandstorm that wouldn't have harmed an infant. Nobody here faced a single danger that he had not brought with him.

Would it be like this forever? Men traveling enormous distances to face themselves?

There had been little work done since noon today. Shute had given up on that. On a stack of walls sat Timmy, practically surrounding the buggy-pickup radio, surrounded in turn by the bubble's population.

Timmy stood up as Shute approached the group. "They're gone," he announced, sounding very tired. He turned off the radio. The men looked at each other, and some got to their feet.

"Tim! How'd you lose them?"

Timmy noticed him. "They're too far away, Mayor."

"They never turned around?"

"They never did. They just kept going out into the desert. Alf must have gone insane. Carter's not worth dying for."

Shute thought, But he was once. Carter had been one of the best: tough, fearless, bright, enthusiastic. Shute had watched him deteriorate under the boredom and the close quarters aboard ship. He had seemed to recover when they reached Mars, when all of them suddenly had work to do. Then, yesterday morning- murder.

Alf. It was hard to lose Alf. Lew had been little loss, but Alf-