As they stepped back into the tunnel the pyramid jerked heavily, throwing them against the wall. Deep fissures had appeared in the cement. They ran along it, Maitland and Lanyon helping Patricia Olsen. Halfway down the tunnel they felt a second tremendous wrench that threw them onto their knees. Looking back, they saw a short section of the corridor buckle, its walls twisted like cardboard. At the same time, once again they heard the sound of the wind hammering past.

They reached the doorway at the far end. Inside, as Maitland had anticipated, the corridors had drained but the bulkheads were still sealed behind the breastwork.

As he looked back for the last time down the tunnel, Maitland saw the section 20 yards away abruptly rise up into the air like the limb of a drawbridge. For a moment there was a cascade of masonry and ruptured steelwork, and then the entire tunnel fell back to reveal a blinding sweep of daylight. Sucked out of the still intact section of tunnel attached to the bunker, air swept past Maitland under pressure, and he was dragged forward a dozen feet before he held himself against a step in one of the walls.

Through the open aperture he looked out into the huge ravine below, like the hundred-yard-wide trench working of a six-lane underpass. Dust and exploding gravel obscured its sides, bursting through the narrowing venturi, but he could see the great bulk of the pyramid towering overhead. The ravine led directly below it, but at least two-thirds of its base still rested on solid earth, the overhanging portion revealing the L-piece of the communicating tunnel jutting below. The pyramid had tilted by a full ten degrees, snapping the tunnel in half like a straw.

Peering up, Maitland tried to identify the observation window in the apex, but it was hidden behind the dark clouds of detonating grit.

"Maitland!" he heard someone shout behind him, but he felt unable to tear his eyes from the spectacle before him. Like some enormous wounded mastodon, the pyramid reared up into the storm wind, the precarious shelf of ground on which it rested being cut away yard by yard as Maitland watched. The ravine deepened as the channel grew wider, now that the obstruction of the bunker system had been passed. For a few seconds the pyramid poised precariously, tipping slowly, apparently held by the adhesive forces of the ground below the small portion of its base still fastened to the supporting shelf.

Then, with a sudden final lurch, it toppled over the edge, and in a blinding explosion of dust and flying rock it fell sideways into the ravine. For a few moments its massive bulk rose over the clouds of debris, its apex pointed obliquely downward, resting on its lef thand face. Then the wind began to cover it, burying it completely beneath vast drifts of dust.

Stunned, Maitland gazed out at the scene of this cataclysmic convulsion. At his shoulder he found Lanyon, his arm around Patricia Olsen, with Waring behind them. Together they stared down into the ravine, watching the dust clouds pour past at incredible speed. Then numbly the little group withdrew along the short stump of tunnel and made its way into the corridor.

Waring and Patricia Olsen sat down on the top step of the stairway. Lanyon leaned against the wall, while Maitland squatted on the floor.

"I guess you've got your story, all right, Pat," Lanyon said to the girl.

She nodded, pulling the hood of her jacket closer around her cold face. "Yes, and maybe I can even believe it now. Just about the end to everything."

"What do we do now, Commander?" Waring asked. "We're not really much better off, are we? It's only a matter of hours before this place starts breaking up like a derelict wreck."

Lanyon pulled himself together. On either side heavy bulkheads sealed the two corridors branching off from the stairway, huge cement-filled sandbags blocking their approach. He and Maitland examined the cracks appearing in the ceiling. Forced by their own weight, no longer supported by the surrounding earth, the bunkers were breaking apart. As Waring had said, soon the staircase and the segments of corridor would detach themselves and fall onto the floor of the ravine 6o feet below.

"I'll try the stairway," Lanyon told the others. "There's a chance we may be safer down below."

Stepping past Pat Olsen, he began to make his way around, peering through the thin light. He had almost completed one circle when his foot plunged through the surface of a pool of water. Reaching down with his hands, he found that the stairwell was full. The three levels below had been completely flooded.

He rejoined the others. They had moved into the left-hand corridor, were pressed against the collapsing breastwork of sandbags. Maitland gestured Lanyon over quickly. Looking up, he saw that one of the cracks across the roof of the stairway was now two feet wide, a deep fissure in the thick concrete now widened perceptibly, moving in rigid jerks as the reinforcing bars snapped one by one like the teeth of a giant zip.

Suddenly, before he expected it, the entire corner section of the bunker containing the stairway and the recess between the corridors twisted and slid away into the ravine, sending up a tremendous cloud of white dust. A narrow projection of ceiling separated them from the open air stream, but above this was another toppling piece of masonry, a huge section of the original wall pivoting on its stem of reinforcing bars. Most of these had snapped, and the giant slab, a block weighing 15 or 20 tons, was slowly tilting down over them.

Seeing it, Patricia Olsen began to scream helplessly, but Lanyon managed to steady her for a moment, looking around desperately for some way of escape. Their only chance seemed to be to slide down into the ravine, then hope they would find some narrow crevice where they could shelter from the monster poised above them.

Quickly he seized Patricia's arm, began to pull her toward the edge. She dug her heels in desperately, still clinging to the temporary safety of the ledge.

"No, Steve! Please, I can't!"

"Darling, you've got to!" Lanyon bellowed at her above the roar of the wind. He twisted her arm roughly, dragging her with him, holding the ragged ledge with his free hand before pushing her over.

"Lanyon! Wait!" Maitland grabbed his shoulder, then pulled Patricia back before she could fall. "Look! Up there!"

They craned upward. Miraculously, the great wall section towering above them was slowly keeling backward away from them into the wind. Showers of stones and flying pieces of rubble cascaded across its exposed surface, but by some extraordinary reversal of the laws of nature, it was no longer yielding to the greater force of the wind.

Amazed, they looked up at this incredible defiance, intervening like some act of God to save them.

Suddenly Maitland shouted out into the air, began to pound insanely on the wall of the ledge. For a moment he raged away hysterically, and then Lanyon and Waring held his arms and tried to calm him.

"Hold it, Doctor," Lanyon roared into his face. "Don't be a fool. Control yourself!"

Maitland shook himself free. "Look, Lanyon, up there! Don't you realize what's happened, why that wall fell away from us, _into_ the wind? Don't you see?" When they frowned at him in bewilderment he shouted, "_The wind's dropping!_ It's finally spent itself!"

Sure enough, the great fragment of wall was moving slowly forward into the face of the wind. Maitland pointed at the sky around them. "The air's lighter already! The wind's dying down, you can hear it. It's finally subsiding!"

Together they looked out across the ravine. As Maitland had said, visibility had now increased to over 6oo yards. They could see plainly across the black fields beyond the estate, even trace the remains of a road winding along the periphery. The sky itself had lightened, was now an overcast gray, the sweeping pathways across it inclined slightly downward.