Now the garage was deathly silent and still. It seemed to have taken hours to purge the spacesuit tanks of their low-pressure mix and refill them with room air. Then getting into the damned suits took even longer. The metal shell of the torso and leggings were unaffected by the additional air pressure, but the gloves ballooned so badly they looked like boxers' mitts, and all the suit joints were painfully stiff. It's like we've all got arthritis real bad, Deems thought.

He watched four members of his team checking out the cutting laser, clumsy and slow in the overpressured suits. The laser looked heavy and sinister, mounted on a tripod like some kind of gun. Clusters of power condensers and cooling blades lined its length. Another pair from their group sat on the rock floor awkwardly connecting power cables together.

Who the hell got himself caught in a suit out here? he wondered. Personnel claimed they checked out everybody working in the garage, they all got into tunnels one and two okay. And the only guy on the surface made it to the rocket port, so he's accounted for. Somebody's miscounted or screwed up someplace.

Tunnel four was two hundred yards long, Deems knew. Twice the length of a football field. They were going to lug the laser down to the sealed EVC hatch at the end of the tunnel, dragging the cable along, and start cutting the hatch open.

And when we do, he said to himself, we'll be killing anybody inside the EVC. He glanced at the three empty suits on the floor by the hatch. Shaking his head inside his helmet, Deems thought that the suits would be about as much good as an umbrella in a typhoon.

The Stavenger kid's gonna die, he thought We'll get the two who're trying to wipe us out, but we're going to kill the Scavenger kid in the process.

"Did you hear that?" Melissa asked, looking up toward the rock ceiling of the EVC, lost in the shadows beyond the strips of overhead fluorescent lamps.

Greg was hunched over the display screens at the front of the chamber. Tunnel four was almost a vacuum, and although somebody had shut all the airtight hatches in the other tunnels, the oxygen level in tunnel three was sinking nicely.

"Hear what?" he called to Melissa.

"It sounded like-"

"Wait!" Greg snapped, silencing her. "Listen!"

Melissa walked to his side. She felt utterly weary. Her knuckles were skinned, her hands greasy, her clothes a mess. She had stripped off her jacket, and now she felt chilled in nothing but the light sleeveless blouse she had worn beneath it.

Greg tapped on the keyboard and the display screen showed the tunnel outside. Four people in spacesuits were aiming a heavy cutting laser at the EVC hatch.

"They're trying to get through the hatch," he whispered.

Melissa stood by him and glanced again up toward the shadowy ceiling. She thought she had heard something from up above, but in this echoing cavern, maybe it was a noise from the tunnel outside that had caught her ear.

Greg laughed, shakily. "It'll take them hours to burn through the hatch," he said. "I know the kinds of lasers they use for cutting metals."

It sounded less than reassuring to Melissa. "I thought you said they couldn't get through the tunnel at all."

"They must have set up a death squad," he said. "They're just killing themselves faster, that's all."

Doug clamped his penlight in his gritted teeth and tried to work the edge of the power drill into the dust-caked rim of the access panel. Things don't rust up here, he thought, but the dust packs as solid as concrete after a few years.

He had carefully removed the hinges from the access panel, trying to do it as quietly as he could. Surprise is still a weapon, he told himself. As long as they don't know I'm here I've got an advantage over them.

Perspiration stung his eyes but he kept levering the power drill with both hands, using the drill like a miniature crowbar, trying to pry the damned panel loose. Does Greg have any weapons with him? he suddenly wondered. As far as Doug knew there wasn't a gun anywhere on the Moon. The worst Greg might have would be a steak knife from The Cave. Or a wrench that he could use as a club.

The panel creaked a little. Doug saw light seeping into the vent from below. Worming the point of the drill deeper into the crack he had created, he struggled to his knees-head bent to keep from banging the top of the vent-and leaned all his weight on the tool, wishing for once that they were on Earth where his weight counted for more.

Groaning, the panel edged up an inch or so. Doug grabbed its edge with both hands and pushed, straining so hard he felt pain across his shoulders and down his back.

With a final shriek of protest the panel opened all the way. Doug pushed it clattering aside and looked down into the environmental control center. A pump's disassembled parts lay scattered oh the stone floor twenty feet below him. He could see another pump, apparently still working, on the side of the narrow walkway. No sign of Greg or Melissa, though.

The walkway down there looked very tight. If I don't hit it just right I'll land on the pump or the pieces Greg's strewn across the floor. I could break an ankle. Or my neck.

But there was no time to hesitate. Twenty feet down. You're on the Moon; you can drop twenty feet with no sweat. Still, Doug grabbed the edge of the open access hatch and lowered himself slowly, hanging by both hands for a moment Then he saw Greg, only ten yards away, by the front hatch. And Greg, turning suddenly, saw him.

Doug let go and started to drop with the dreamlike slowness of lunar gravity to the walkway below. Greg howled madly, grabbed a heavy wrench and threw it at his brother.

Doug felt his left arm shatter with pain as he hit the floor, slipped on a loose piece of junk, and went down flat on his back. As he fell he saw Greg grab for another weapon.

ENVIRONMENTAL CONTROL CENTER.

It was Doug!

Greg turned at the blood-freezing screeching noise of metal grinding against metal and saw his half-brother hanging like an ape from the ceiling. Then Doug let go and dropped slowly, like a monster in a nightmare, toward the floor. Howling, Greg reached for a wrench and threw it at Doug, then leaped to the workbench and grabbed the first tool his hand could reach, a screwdriver, smaller, but comfortably heavy.

Melissa stood frozen against the workbench, screaming, "Get him! Get him!"

Greg saw that Doug had sprawled on his back. Got to put him out before he can get to his feet, Greg told himself. He leaped toward his fallen brother.

Through pain-hazed eyes, Doug saw Greg springing at him. There was no room on the confined walkway to do more than turn on his side, no place to hide or even dodge.

Greg landed on Doug's side with a thump that drove the air from Doug's lungs. He tried to shield himself, but his left arm wouldn't work. He could hardly move it.

Greg held the screwdriver like a knife up above his head and stared down into his half-brother's pain-widened eyes. For an instant he hesitated. Melissa was screaming something. Greg saw not Doug, but Paul Stavenger looking up at him accusingly. Murderer! he heard Paul call him. You murdered me once and now you're going to do it again.

Through pain-hazed eyes Doug saw his half-brother hesitate, the screwdriver held over his head like a dagger. Pushing Greg's weight off him, Doug reached up with his good arm and grabbed Greg's wrist.

It was a nearly equal contest. Doug's left forearm was broken, but he was stronger, more muscular than Greg. Gripping Greg's wrist, Doug pulled himself up to a sitting position, forcing Greg backwards. Then he began bending Greg's wrist back slowly, slowly, until Greg grunted and dropped the screwdriver.

The two brothers sat on the cold stone floor, gasping, glaring at each other.

"How'd you get in here?" Greg growled.

"Vents," Doug panted. "Plasma torch exhaust vents."

"What do you think... you're going to... accomplish?"

Doug pointed with his good hand toward the hatch up at the front of the EVC. "They'll be breaking through," he said, breathing raggedly. "When they do... we're all dead. The tunnel's... almost down to vacuum."

Suddenly Doug's world exploded. Flashes of light burst before his eyes and then it all went utterly black.

He slumped over, the back of his head oozing blood. Greg looked up and saw Melissa standing triumphantly over them, a heavy wrench grasped tightly in both her gaunt hands. The wrench was stained with Doug's blood.

"That takes care of him," she snarled.

Greg climbed slowly to his feet "You heard what he said," Melissa urged. "They're going to kill us when they get the hatch open."

"We're trapped in here," Greg said, looking around wildly. "There's no way out."

"Then let's finish what we came here for."

"We won't have time!"

"We've got to!"

Another thumping sound from the hatch.

"They're going to burn through it," Greg said, his voice shaking. He looked down at Doug again; his half-brother seemed dead.

"Do something!" Melissa shouted.

Greg tried to clear his thoughts. "He came through the old plasma vents...' Straightening up, Greg went to the computer by the workbench. "Those vents open to vacuum! If I can open them all, it'll suck all the air out of the base in a few minutes."

Melissa's eyes glowed. "That'll do it!"

Greg began scrolling through the computer programs, searching for the controls to the plasma vents.

Doug couldn't focus his eyes. Everything was a blur, a red smear. Blinking, coughing, he pushed himself up to a sitting position and slumped against one of the pumps. He wiped at his eyes with his good hand and they came away sticky with blood.

Far, far away he saw a slim figure bent over a glowing computer display screen. Greg. Someone was standing beside him but his vision was too blurred to make out who it might be.

"Hurry!" she was saying, her voice pitched high and shrill. "Hurry! I can hear them outside the hatch!"

"I've got it," Greg said, his voice as calm and implacable as death.

"Greg...' Doug croaked, his throat raw. "Don't..."

Greg turned and his eyed flashed wide. "I thought she'd killed you."

"Don't do it," Doug said again. "You'll be killing Mom."

He saw his brother's eyes widen slightly. But then Greg said, "What of it?"

Doug pushed himself to his feet, feeling slightly dizzy. He reached out a hand to steady himself against the gutted shell of a pump.

"Stay away," Greg warned, growling. Yet his fingers hesitated over the keyboard.

Melissa tried to push him away. "If you won't do it, I will," she snarled.

Strength was returning to Doug's legs. The pain hi his left arm was bearable, a sullen throb. His vision had cleared and he felt stronger with each step he took toward the pair of them.

"Stop it, Greg. Stop it now while you can. Put an end to the killing."

I'll put an end to everything!' Greg snapped. But he stared at his brother without touching the keys that would open the plasma vents.

"No, you don't want to do that, Greg. You can't destroy Moonbase. It means too much to everyone on Earth. It means the future of the human race."

"The human race!" Melissa laughed bitterly. "The world would be better off if the human race were wiped out to the last pitiful one."

Doug was almost within arm's reach now. The nano-machines had stopped the bleeding from his scalp wound, repaired the blood vessels in his brain that Melissa's blow had ruptured. They were even beginning to knit together the fracture in his forearm.

"I'm warning you!" Greg screeched. "Stay away from me!"

"Just back off from the computer, Greg," Doug said as softly as he dared. "Go to the hatch and tell them you're coming out peacefully."

"No!"

"You've got to, Greg. This isn't just between you and me. There's more than our lives involved here, much more."

Greg took an uncertain, lurching step backwards, like a drunk too addled to understand what he was doing.

"Coward," Melissa hissed. She stabbed a finger toward the keyboard.

Doug lunged forward blurringly fast and caught her frail wrist 'No," he said. "You're not going to destroy us."

"Leave her alone!" Greg threw himself at Doug, clawing at his throat Melissa scratched at Doug's face with her free hand.

He staggered back under their assault, flung Melissa aside like a rag doll and grasped one of Greg's strangling hands. His brother was trying to choke him. Beyond his insanely twisted face, Doug could see Melissa reaching for the keyboard again.

Doug jabbed a thumb in Greg's eye. He howled and released Doug's throat Stepping back just enough for the leverage, Doug punched his brother in the jaw with a short, compact right Greg's eyes rolled up and he collapsed to the stone floor.

Melissa was banging on the keyboard, desperately hoping to strike the key that would open the plasma vents to vacuum. Doug reached for her again when suddenly the big chamber seemed to erupt into a tornado. Dust swirled as Doug's ears roared painfully.

He saw Melissa's face, glowing with triumph, crumble into a mask of blood. Blood gushed from her ears, her eyes. Her mouth filled with blood as she twirled in the rushing air, and slid across the floor, arms flapping like a scarecrow's.

Doug had only a moment to turn and look down at Greg, bleeding from every pore, before he too collapsed and died.

MOONBASE INFIRMARY.

Douglas Scavenger was sitting up in the bed, tubes carrying whole blood, saline solution, and liquid nutrient into his arms, monitoring machines above his head blinking and displaying crawling, glowing lines that represented his heart beat, breathing rate, blood pressure. Each factor was so high that the monitors had been specially programmed so that they would not constantly be screeching their warning signals.

His mother was sitting on a hard plastic chair at the foot of the bed while Zimmerman stood beside the bed, scowling at him.

"The nanomachines have raised your metabolic rate by a factor of nearly three," he muttered. "I don't understand it."

Joanna said softly, "They saved his life; that's enough for me."

"Yah, but how?" Zimmerman insisted. "How did they do it?"

"Don't ask me," said Doug. "One moment I was passing out in the EVC. The next thing I knew, I woke up here in the infirmary."

Still scowling, Zimmerman mumbled, "They must have shut down your heart rate to lower your blood pressure and prevent ruptures of the capillaries."

"How did they know to do that?" Doug asked.

Zimmerman looked down at him. "How did they make the decision to suspend your heart function? Did they simply react to the immediate physical stimulus, or...' His voice trailed off.

"Or what?" Joanna asked.

With a shake of head hard enough to make his jowls waddle, Zimmerman continued, "Or did they make an assessment that it was safer to shut down your heart than to allow your capillaries to burst?"

"Make an assessment?" Doug echoed. "Like they're intelligent?"