The rough, curving walls were glistening with moisture, though the air current surging up from the depths at the command of some extractor plant behind them was dry and arid. Increasingly, the two of them were aware of the relentless cold pressure of those countless tons of water leaning, day in and day out, on the roof of the fortress. And as though to underline the point, the string of low power naked bulbs set in the slanting ceiling of the stairway dimmed abruptly and then slowly flared again - though not quite to their former brightness, the girl thought with a shiver. Still, it was probably just some fluctuation in the output of the reactor below them... The sound of voices above swelled; the echoes expanded, then dwindled as the people talking passed the entrance to the shaft and continued on around the passageway.

They crept into the reflected light from the landing on B Level. Footsteps and voices echoed here too, advancing and receding in some numbers. Elevator doors opened and shut and they heard the cages whining away upwards beyond the wall of their stairway. It was some minutes before Kuryakin was satisfied that it was safe to peer around the last corner and prospect the landing. He drew back suddenly. A solitary man was waiting for an elevator to return.

Two minutes later, after the doors had hissed shut and the lift had ascended again, be ventured to peer once more. The landing was empty.

Beckoning to the girl to follow him, he raced across and plunged down the further flight of stairs towards the bottom level. Here it was quieter, the lights were even dimmer, and there was no sign of any of the fortress's inhabitants.

There was no sign, either, of Napoleon Solo. There were six featureless cells in the cul-de-sac leading off the circular passage. And all of them were empty.

"What now?" Coralie asked, seeing the momentary flicker of despair on Illya's face. "Is there anywhere else we can look for your friend?"

He shook his head slowly, his eyes somber. "Anywhere," he said. "He could be anywhere… alive or dead. We shall simply have to proceed with the action as though -"

"But I thought your friend -"

"The mission," Illya said almost savagely. "The mission comes first. I told you what Waverly said. We'll try to get back to the control room on the top floor and see what we can do there."

They completed the circuit of the corridor, past a half-open door hedged with red notices warning unauthorized personnel without protective clothing to keep out - and through which they glimpsed behind coils of tubing a segment of the great reactor's silver sphere. As they approached the elevators again, they saw a number of trucks drawn up in two ranks facing an immense pair of doors on rails. To Kuryakin's astonishment, there seemed to be no guard, no sentry box, only a series of metal housings flanking the doors with inset magic eye discs and an old-fashioned set of stop-go lights.

"The whole thing's electronically controlled," he said softly. "If we only could get to that control room… Come on!"

They skirted the empty trucks and gained the stair case. By the time they reached the A Level again, they were both panting. But they were in luck: they had seen nobody. "Come on," the Russian urged again. "The door's a little way further around the curve, on the inside wall. I saw it in the distance when we left the briefing room."

Suddenly - bullets splatted against the concave surface of the outer wall. Simultaneously, from behind them, the sharp crack of an automatic, three times, reverberated in the narrow corridor.

"Run!" Illya yelled, hauling her after him, pelting further, further, further around the curve of the convex inner wall. The uniformed officer he had seen out of the corner of his eye as he glanced over his shoulder fired again and again, trying to hit them with ricochets off the outer wall now that they were invisible to him.

As they ran, voices shouted. Footsteps started after them from somewhere out of sight. A door in the outer wall opened and two women in D.A.M.E.S uniform emerged just in front of them. One was carrying a black frogman suit over her arm.

"Apologies, madam," Kuryakin said hurriedly as he snatched the heavy rubber garment from her hands, twisted it around her head and pushed her, reeling, across to the other side of the passage. The second woman swore violently and began to tug something from the pocket of her uniform jacket. Without breaking her stride, Coralie Simone slashed a backhanded blow across and caught her Karate-style on the side of the neck. She dropped straight to the floor, rolled against the calves of the woman struggling to free herself from the folds of the diving suit, and brought her down too.

Kuryakin and the girl sprinted on. The shooting from behind had stopped when the marksman had come into sight of the two D.A.M.E.S. But now there were heavy footsteps pounding towards them from around the curve ahead. A deeper report thundered in the confined space and a slug chiseled a groove in the wall beside Coralie's head.

"I was afraid of that," the agent panted. "Sent… friend... around the other way... cut us off." He dropped to one knee. Along the surface of the outer wall where it curved out of sight ahead of them, a grotesquely distorted shadow was approaching. He sighted along the barrel of the PPK and fired.

There was a puff of plaster dust where the bullet gouged itself a channel. Before the screech of the ricochet had died away, both footsteps and shadow had halted. Behind, too, there was silence now.

"Let's go," Illya whispered, his lips close to Coralie's ear, "before they realize they can sidle up to us along the inner wall. If the control room door's near enough, we'll reach it before we come in sight of the man ahead of us."

"Suppose it's locked?" the girl murmured as they began to move.

Illya merely shrugged. There were more footsteps in the distance now, and a susurrus of low voices asking questions somewhere in the circle of corridor behind them.

Backs to the inner wall, they inched towards the elusive door. Slowly, inexorably, the corridor uncoiled before their advance... and as relentlessly, the inner wall remained exasperatingly blank.

With a lightning-like pounce, Kuryakin leaped suddenly to the far side and ripped off a shot, left, right, each direction. There was a distant scrambling of feet as he jumped back again, a single shot from their left, the bigger caliber gun with the deeper tone, and then a cry of protest from the other side as the slug screamed to the right.

"They're too close up to shoot at us now, really," Illya said. "Every shot's in danger of bouncing on and hitting their own people around the curve… The door's not far now: I could see it from the other side."

And sure enough, the heavy flush-fitting steel door, like the entrance to a warship's cabin, was soon sliding around the curve towards them. Once it was fully in view, the Russian sprang forwards and grasped handle. It turned easily in his grip and the door swung inwards. With a gasp of relief, he motioned the girl through, closed the door, and dropped two steel struts in place across it. They were in.

The door admitted directly to a narrow gallery which ran all the way around the walls of a huge circular room on the floor below. Halfway around to the left, a staircase spiraled to the lower floor; and opposite this to the right the gallery bore a glassed-in projection resembling the control room of a television or recording studio. Through the huge panes, they could see colored lights winking, the gleam of stainless steel levers, banks of bright terminals. There were a number of desks with telephones on them distributed about the floor space below, but the majority of the enormous room was occupied by a circular table so vast that the seven people grouped along one sector of it were dwarfed by its size.