"Be careful."

"That's why I want the chair."

Jim came back with one; the doctor went through the pressure lock again. He came back in about five minutes later. "It's a booby trap," he stated.

"What do you mean?"

"Beecher didn't try to keep men outdoors all night-at least I don't think so. It's automatic. They've put an electriceye grid across the door. When you break it, a bolt comes across, right where you'd be if you walked through it." He displayed half a dozen deep bums through the chair.

Marlowe examined them. "But that's not the important point," MacRae went on. "It's automatic but it's inflexible. It hits about two feet above the step and about four feet. A man could crawl through it-if his nerves were steady."

Marlowe straightened up. "Show me."

They came back, with the chair still more burned, in a few minutes. "Kelly," Marlowe said briskly, "I want twenty volunteers to make a sortie. Pass the word around."

There were at least two hundred volunteers; the problem was to weed them down. Both Frank and Jim tried to get in on it; Jim's father refused to take any but grown, unmarried men -except himself. MacRae he refused.

The doctor pulled Jim back and whispered to him. "Hold your horses. In a few minutes I'll be boss."

The raiding party started into the lock. Marlowe turned to MacRae. "We'll head for me power plant. If we are gone more than two hours, you are on your own." He went into the lock and closed the door.

As soon as the door was closed, MacRae said, "Okay, twenty more volunteers."

Kelly said, "Aren't you going to wait two hours?"

"You tend to your knitting! When I'm out of here, you're in charge." He turned and nodded to Jim and Frank. "You two come along." MacRae had his party in short order, had apparently selected them in his mind before Marlowe left. They filed into the lock.

Once the outer door was open MacRae flashed his torch into the street. The Pottles and the unfortunate Joseph Hartley lay where they had fallen, but no other bodies littered the street. MacRae turned around and said, "Ginune that chair. I'll demonstrate the gimmick." He stuck it out into the door. Instantly two bolts cut across the doorway, parallel to the ground. After they were gone and the eye was still dazzled by their brilliance, two soft violet paths of ionization marked where they had been and then gradually dispersed.

"You will note," said the doctor, as if he were lecturing medical students, "that it does not matter where the chair is inserted." He again shoved the chair into the opening, moved it up and down. The bolts repeated at split-second intervals, but always at the same places, about knee high and chest high.

"I think it is best," continued the doctor, "to maintain the attack. Then you can see where you are. First man!"

Jim gulped and stepped forward-or was shoved, he was not sure which. He eyed the deadly fence, stooped over, and with awkward and infinite care stepped through. He went on out into the street. "Get moving!" the doctor ordered. "Spread out."

Jim ran up the street, feeling very much alone but terribly excited. He paused short of the end of the building and cautiously looked around the comer. Nothing either way-he stopped and waited in the darkness, ready to blast anything that moved.

Ahead of him and to the left he could see the curious structure which had almost cost him the top of his head many hours before. It was clear now that the bolts were coming from it.

Some one came up behind him. He whirled and heard a voice yelp, "Don't shoot! It's me-Frank."

"How about the others?"

"They're coming-I think."

A light flashed at the building ahead, beyond the shield from which the bolts came. Frank said, "I think somebody came out there."

"Can you see him? Do you think we ought to shoot?"

"I don't know."

Someone else was pounding up the street behind them. Up ahead, from near the spot where Frank had thought he had seen a man a heater flashed out in the darkness; the beam passed them.

Jim's gun answered by pure reflex; he nailed the spot from which the flash had come. "You got him," said Frank. "Good boy!"

"I did?" said Jim. "How about the guy behind me?" He found that he was trembling.

"Here he is now."

"Who shot at me?" the newcomer said. "Where are they?"

"Nowhere at the moment," Frank answered. "Jim nailed him." Frank tried to peer into the mask; the night was too dark. "Who is it?"

"Smitty."

Both Frank and Jim gave exclamations of surprise-it was Smythe, the practical man. "Don't look at me like that," Smythe said defensively. "I came along at the last minute-to protect my investment. You guys owe me money."

"I think Jim just paid it off," suggested Frank.

"Not on your life! That's another matter entirely."

"Later, later," said Frank. Others were coming up. Presently MacRae came puffing up and roared, "I told you birdbrains to spread out!" He caught his breath and said, "We tackle the Company main offices. Dogtrot-and don't bunch together."

"Doc," said Jim, "there are some in that building up ahead."

"Some what?"

"Somebody that shoots at us, that's what."

"Oh. Hold it, everybody." MacRae gave them hoarse instructions, then said, "Got it, everybody?"

"Doc," asked Frank, "how about the gun over there? Why don't we wreck it first?"

"I must be getting old," said MacRae. "Anybody here enough of a technician to sneak up on it and pull its teeth?"

A faceless figure in the darkness volunteered. "Go ahead," Doc told him. "We'll cover you from here." The colonial trotted ahead, swung around behind the shield covering the stationary automatic blaster, and stopped. He worked away for several minutes, then there was a white flash, intensely bright. He trotted back. "Shorted it out. Bet I blew every overload breaker in the power house."

"Sure you fixed it?"

"You couldn't dot an T with it now."

"Okay. You-" MacRae grabbed one of his squad by the arm. "-tear back and tell Kelly that allee allee out's in free. You-" He indicated the chap who had wrecked the gun. "-go around in back and see what you can do with the setup back there. You two guys cover him. The rest of you follow me-the building ahead, according to plan."

Jim's assignment called for sneaking along the face of the building and taking a covering position about twenty feet short of the doorway. His way led him over the ground where the man had been at whom he had shot. There was no body on the pavement; he wondered if he had missed. It was too dark to look for blood.

MacRae gave his covering troops time to reach their stations, then made a frontal assault with six to back him up, among them Frank. The doctor himself walked up to the building entrance, tried the outer door. It opened. Motioning the assault group to join him, he went in. The outer door of the building's lock closed on them.

Jim huddled against the icy wall, eyes wide, ready to shoot. It seemed a cold eternity that he waited; he began to fancy that he could see some traces of dawn in the east. At last he saw silhouettes ahead, raised his gun, then identified one as Doc's portly figure.

MacRae had the situation in hand. There were four disarmed prisoners; one was being half carried by two others. 'Take 'em back to the school," Doc ordered one of his group. "Shoot me first one of them who makes a funny move. And tell whoever is in charge back there now to lock 'em up. Come on, men. We've got our real job ahead."

There came a shout behind them; MacRae turned. Kelly's voice called, "Doc! Wait for baby!" He came running up and demanded, "What are the plans?" Behind him, men were pouring out of the school and up the street.

MacRae took a few minutes to recast things on the basis of more guns. One of the platoon leaders, a civil engineer named Alvarez, was left in charge at the school with orders to maintain a guard outside the building and to patrol the neighborhood with scouts. Kelly was assigned the task of capturing the communications building which lay between the settlement and the space port. It was an important key to control of the whole situation, since it housed not only the local telephone exchange but also the radio link to Deimos and thence to all other outposts on Mars-and also the radar beacons and other aids for incoming ships from Earth.