Two hours later they had their first sight of Hardoon Tower.

Maidand was doing his 15-minute turn at the periscope when the operator told him that they had entered the zone of maximum signal strength.

"Could be anywhere within a couple of square miles of here," be reported, swinging the direction-finder aerial without influencing the volume. "From now on we'll have to make visual contact."

Maitland peered through the periscope. Ahead the roadway had broadened into a furrowed band of shattered concrete and wire mesh about 1 oo yards wide, stained with huge white and gray patches which suggested some enormous roadwork had recently been in progress. The tractor edged forward along the center at 15 mph, tacking from left to right across the band. Two hundred yards away the road disappeared into the dim whirling mass of the wind stream. Beside the roadway the ground was black and dark, devoid of all vegetation, dotted with a few huge rolling objects, stumps of giant trees, blocks of masonry, all moving from left to right across their path.

Ahead, high in the air, something loomed for a moment, a lighter patch of sky, apparently an interval in the dust cloud. Maitland ignored it, searching the ground carefully for any hidden side turning.

A few seconds later he realized that the strip of lighter air was still in front of him.

Straight ahead, its massive bulk veiled by the duststorm, an enormous pyramidlike structure reared up, its four-angled sides 100 feet across at the base, tapering to the apex 80 feet above. The tractor was now about a quarter of a mile away and, although partly obscured, the pyramid was the first structure Maitland had seen for weeks which retained hard clean outlines. Even at this distance he could see its straight profiles, the perfectly pointed apex, cleaving the dark air stream like the prow of a liner.

He gestured Halliday over to the periscope. As the captain whooped in surprise, Maitland gestured to Lanyon.

"It looks as if Hardoon's strongpoint is up ahead. About three or four hundred yards away. A huge concrete pryamid."

"It's fantastic," Halliday said over his shoulder, centering the periscope. "Who does the maniac think he is-Cheops? Must have taken years to build."

He handed over the periscope to Lanyon, who nodded slowly. "Either years or thousands of men. The roadways indicate there's been a pretty big construction force on the job."

They edged nearer the pyramid; its great bulk rising above into the flickering sky. Two hundred yards away the tractor struck a low obstacle with its offside front track, and they looked down at a low wall, ten feet high, rising out of the ground and running in the direction of the left-hand corner of the pyramid. The wall was ten feet wide, a massive reinforced concrete buttress. As they moved along it, a second rampart appeared out of the gravellike soil on their right, and they found themselves entering a long approach system of parallel concrete walls, partly intended as windbreakers for the pyramid, and partly to screen entering vehicles.

Maitland searched the face of the pyramid for apertures, but its surface was smooth and unbroken. Gradually, as the height of the supporting walls increased, it was lost from sight and they entered a narrow ramp that led below an overhanging shoulder and then around a right-angle corner into what appeared to be a dead end.

Halliclay tilted back the periscope, craning to look up at the great bulk of the pyramid obscured by the stream of dust and gravel cascading across its surface.

"Looks as if this isn't an approach road after all," Halliday commented. "No entrance bays or locks. We'll have one hell of a job reversing out of here. Why don't they put up some signs?"

Suddenly they swayed on their feet, grabbed at the ceiling straps. The tractor had dropped abruptly, was moving steadily downward like an elevator.

Maitland dived for the periscope, just in time to see the walls around them soar upward into the air, the apex of the pyramid disappear. Seconds later the rectangular outlines of an elevator opening rose above them. The black sides of the shaft ran past, then slowed down as the elevator reached its floor. A horizontal lock slid across the opening and sealed it, shutting out the daylight.

"Well, they must be friendly," Halliday decided. "I was beginning to wonder how we'd get in if they didn't want us."

The driver cut the engines, and as the din subsided they heard mechanics outside the tractor shackling exit ladders to its turret. Halliday began to unlock the hatchway, motioned to the others to get to their feet.

"Stretch your legs, everybody. May be our last chance for days."

He opened the hatch, raising it a few inches, and someone on the roof pulled it back. He climbed out, followed by Maitland and the radio operator.

The tractor was at the bottom of a large freight-elevator shaft, part of an underground bunker from which high driveways led off to dark transport bays. Men in black plastic suits and helmets stood around the tractor, most of them with holsters on their belts. Maitland recognized the uniforms he had seen in Marshall 's Park Lane basement.

As he swung down, a tall, rough-featured man with a white pyramid-shaped triangle on the front of his helmet stepped over to him.

"What are you clowns playing at?" he snapped. "Why the hell aren't you using your radio?"

His voice was a snarl of irritation and violence. He looked at Maitland, then grabbed him in surprise, glancing up at Halliday, who was helping the radio operator out of the turret.

"What's all this?" the big man snapped. He wrenched Maitland around roughly, fingering his navy weather jacket. "Where's Kroll? He was supposed to bring Symington. Who are all you people?"

"Isn't Symington here?" Maitland asked him.

The big man stared at him angrily, then looked over his shoulder and gestured toward a squad of guards who were encircling the tractor. At the same time he reached for his holster.

Halliday was still standing on the roof, gesturing back the radio operator, who was about to join Maitland on the ground.

The squad of black-suited guards closed in around the Titan, two or three of them swarming up its sides. Maitland found himself seized by the neck, jabbed an elbow into his attacker and fell backward with him against one of the tracks. He kicked himself loose from the man and struck out at two others who closed in on him, butting them with his head. One of them punched him hard in the face, the other grabbed him around the waist and pulled him downward onto the ground again. As he lay there struggling he saw the big guard backing away from the tractor, a heavy.45 automatic in his hand. Everyone seemed to be shouting, and then the.45 roared out twice, the flashes from its barrel lighting up the sides of the Titan.

A figure, apparently Halliday, came lurching down the ladder, stumbled a few feet across the floor and then fell onto its face.

Maitland slammed a fist into the back of one of the men lying across him, managed to free himself for a moment. He was trying to sit forward, when someone ran up and kicked him heavily in the side of the head.

His brain exploding like a roman candle, he fell backward into a deep roaring pool of darkness.