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.