"It's important. I've got to get out of here."

"Then you'll have to walk," said the policeman.

Lucky gritted his teeth with vexation. There was no way of getting through the crowd on foot or on wheels. It had to be by air and it had to be now.

"Isn't there anything available I can use? Anything?" He was scarcely speaking to the policeman, more to his own impatient self, angry at having been so simply duped by the enemy.

But the policeman answered wryly, "Unless you want to use a hopper."

"A hopper? Where?" Lucky's eyes blazed.

"I was just joking," said the policeman.

"But I'm not. Where's the hopper?"

There were several in the basement of the building they had left. They were disassembled. Four men were impressed to help and the best-looking machine was assembled in the open. The nearest of the crowd watched curiously, and a few shouted Jocularly, "Jump it, hopper!"

It was the old cry of the hopper races. Five years ago it had been a fad that had swept the solar system: races over broken, barrier-strewn courses. While the craze lasted, Venus was most enthusiastic. Probably half the houses in Aphrodite had had hoppers in the basement.

Lucky checked the micropile. It was active. He started the motor arid set the gyroscope spinning. The hopper straightened immediately and stood stiffly upright on its single leg.

Hoppers are probably the most grotesque forms of transportation ever invented. They consist of a curved body, just large enough to hold a man at the controls. There was a four-bladed rotor above and a single metal leg, rubber-tipped, below. It looked like some giant wading bird gone to sleep with one leg folded under its body.

Lucky touched the leap knob and the hopper's leg retracted. Its body sank till it was scarcely seven feet from the ground while the leg moved up into the hollow tube that pierced the hopper just behind the control panel. The leg was released at the moment of maximum retraction with a loud click, and the hopper sprang thirty feet into the air.

The rotating blades above the hopper kept it hovering for long seconds at the top of its jump. For those seconds, Lucky could get a view of the people now immediately below him. The crowd extended outward for half a mile, and that meant several hops. Lucky's lips tightened. Precious minutes would vanish.

The hopper was coming down now, its long leg extended. The crowd beneath the descending hopper tried to scatter, but they didn't have to. Four jets of compressed air blew men aside just sufficiently, and the leg hurtled down harmlessly to the ground.

The foot hit concrete and retracted. For a flash Lucky could see the startled faces of the people about him, and then the hopper was moving up again.

Lucky had to admit the excitement of hopper racing. As a youngster, he'd participated in several. The expert "hop rider" could twist his curious mount in unbelievable patterns, finding leg room where none seemed to exist. Here, in the domed cities of Venus, the races must have been tame compared to the bone-breakers in the vast, open arenas of rocky, broken ground on Earth.

In four hops Lucky had cleared the crowd. He cut the motors, and in a series of small, dribbling jumps the hopper came to a halt. Lucky leaped out. Air travel might still be impossible, but now he could commandeer some form of groundcar. But more time would be lost.

Bigman panted and paused for a moment to get his breath. Things had happened quickly; he had been rushed along in a tide that was still whirling him onward.

Twenty minutes before, he had made his suggestion to Morriss. Now he was enclosed in a tube that tightened about his body and drenched him with darkness.

He inched along on his elbows again, working his way deeper. Momentarily he would stop to use the small flash whose pinpoint illumination showed him milky walls ahead, narrowing to nothing. In one sleeve, against his wrist, he held a hastily scrawled diagram.

Morriss had shaken his hand before Bigman had half-clambered, half-jumped, into the opening at one side of a pumping station. The rotors of the huge fan had been stilled, the air currents stopped.

Morriss had muttered, "I hope that doesn't set him off," and then he had shaken hands.

Bigman had grinned back after a fashion, and then he crawled his way into the darkness while the others left. No one felt it necessary to mention the obvious. Bigman was going to be on the wrong side of the transite barrier, the side from which the others were now retreating. If, at any time, the lever at the dome lock plunged down, the incoming water would crush the duct and the walls through which it ran as though they were all so much cardboard.

Bigman wondered, as he squirmed onward, whether he would hear a roar first, whether the surging water would make any hint of its presence known before striking him. He hoped not. He wanted not even a second of waiting. If the water came in, he wanted its work done quickly.

He felt the wall begin to curve. He stopped to consult his map, Ms small flash lighting the space about him with a cool gleam. It was the second curve shown in the map they had drawn for him, and now the duct would curve upward.

Bigman worked himself over to his side and bent around the curve to the damage of his temper and the bruising of his flesh.

"Sands of Mars!" he muttered. His thigh muscles ached as he forced his knees against either side of the duct to keep himself from slipping downward again. Inch by inch he clawed his way up the gentle slope.

Morriss had copied the map off the hieroglyphic charts held up before a visiphone transmitter in the Public Works Department of Aphrodite. He had followed the curving colored lines, asked for an interpretation of the markings and symbols.

Bigman reached one of the reinforcing struts that stretched diagonally across the duct. He almost welcomed it as something he could seize, close his hands about, use to take some of the pressure off his aching elbows and knees. He pressed his map back up his sleeve and held the strut with his left hand. His right hand turned his small flash end for end and placed the butt against one end of the strut.

The energy of the enclosed micropile, which ordinarily fed electricity through the small bulb of the flash and turned it into cold light, could also, at another setting of the control, set up a short-range force field through its opposite end. That force field would slice instantaneously through anything composed of mere matter that stood inits way. Bigman set that control and knew that one end of the strut now hung loose.

He switched hands. He worked his slicer to the other end of the strut. Another touch, and it was gone. The strut was loose in his fingers. Bigman worked it past his body, down to his feet, and let it go. It slid and clattered down the duct.

The water still held off. Bigman, panting and squirming, was distantly aware of that. He passed two more struts, another curve. Then the slope leveled off, and finally he reached a set of baffles plainly marked on the map. In all, the ground he had covered was probably less than two hundred yards, but how much time had it taken him?

And still the water held off.

The baffles, blades jutting alternately from either side of the duct to keep the air stream turbulent, were the last landmark. He sliced off each blade with a rapid sweep of his flash butt, and now he had to measure nine feet from the farthest blade. Again he used his flash. It was six inches long and he would have to lay it along the wall, end over end, eighteen times.

Twice it slipped, and twice he had to turn back to the slightly ragged marking of the last sheared baffle blade, scrambling backward and swearing "Sands of Mars!" in a whisper.

The third time the eighteenth measure landed truly. Bigman kept his finger on the spot. Morriss had said the desired place would be almost directly over his head. Bigman turned on his flash, ran his finger along the curved inner surface of the duct, twisted on to his back.