Napoleon and Illya lay very still and watched the silhouette of the Thrush moving diagonally, somewhat closer to them. But his attention was focused only on his error. Apparently nothing was allowed to be thrown where it could be seen from outside.

He struck another match and searched for the dead butt. When it burned down to his fingers he swore, dropped it, swore again, lit another, and picked up the first one. Then he found the butt and hurried back up the hill to his companion. "Got it," he said. "I don't know whether I'll be able to get the hang of this security nonsense or not. Force of habit keeps taking over."

The other one laughed shortly, stubbed his cigarette out on the rock wall, and said, "Well, we've had our freedom for tonight. Let's get back inside."

The two men faded back into blackness under an overhang of rock, and were gone.

After a few moments, two blobs of shadow rose cautiously from the ground and crept up to the overhang. Even close up the U.N.C.L.E. agents could distinguish no back to the cave it formed. They stepped in.

There was a feeling of space ahead of them, and a breath of warm air smelling of oil and people moved gently past them. They nodded to each other in the darkness, and slowly and silently began to move down the long tunnel into the heart of the mountain.

Chapter 11: "Get Those Intruders!"

Eventually the last of the tropical moonlight faded behind them, and Illya brought out his pocket flashlight. Putting his mouth to Napoleon's ear, he said softly, "I'm going to try the light for a second. Get ready to run."

He aimed the slender cylinder at the floor and pressed the button, tensed and alert for the sound of a guard who would probably shoot at the light. A few seconds passed, and nothing happened. He swung the dim beam up and along the wall, dilated pupils straining to draw in the faint images.

The walls were natural stone, only slightly smoothed in the excavating that had formed the tunnel. Not a door nor a side passage nor a ventilator broke the rough stone as far as he could see. After a few seconds they both moved forward again.

The diffused glow of the pocket light slipped along the lava floor and danced up the walls as they continued their stygian way for what seemed like several minutes. Then an answering glow became visible ahead, and they stopped.

"Well," murmured Napoleon, "I think we've arrived."

"Do we burst in without knocking?"

"I think not. Scarcely polite, not to say probably suicidal. Let's practice our sneaking technique."

"Fine. Keep that quiet pistol of yours handy; we may need to hush someone quickly, and I still haven't seen you use it."

"You've got a silencer—you can be just as quiet as I can."

"Yes, but you went to so much trouble bringing that rocket pistol it would be a shame not to let you use it."

"All right. If we have a choice, I'll go ahead. But if we don't, please don't stand on ceremony."

"Do I ever?"

Napoleon had to admit it was not one of Illya's characteristics, and they moved on.

Used air was still blowing softly in their faces, and they were hoping for a ventilator shaft to give them access to the interior of this sub-volcanic antheap. But it was beginning to appear that ventilation passed in and out through the same passages as personnel in search of a breath of fresh air and a cigarette. This meant a likelihood of guards and similar unpleasant phenomena in the immediate offing.

They stopped.

Napoleon shook his head thoughtfully. "It doesn't seem reasonable," he said, "to have all the foul air in the place blowing out from an inhabited area. Either there are blower vents between us and the lighted area, or the lights are leaking in from adjoining rooms where inhabitation is going on. I think it's worth looking at, anyway."

"Why not?" said Illya. "It's your idea—you go first."

"You've got the light."

"You don't need it now."

Napoleon proceeded, hand on his pistol.

The light did indeed grow stronger—the blue-green of fluorescent tubes somewhere. Then there was a corner in front of them. Both stopped, and Napoleon, who was still in the lead, extended an eye around the end of the wall.

There was a double-width steel door some ten feet farther down to the right of their passage, with eye-level glass panels in each half. Only light could be seen through them. The passage ended there.

He drew back and motioned Illya forward. "We're here," he said. "Take a look."

His partner did, and nodded, then moved cautiously around the corner. A moment later the two agents were looking through the glass panels of the doors into a steel-walled corridor, painted a soft green, lined with single doors, and apparently deserted. The corridor ended at a crossing passage about a hundred feet away.

Very gently, Illya tried the door. It remained closed. Napoleon raised one fist and pantomimed knocking. Illya shook his head, and began looking around the walls. Napoleon knew what he was thinking—that stale air had been blowing from somewhere.

They found the opening almost immediately—no great feat, since it was three feet square and set in the ceiling a few feet above their heads just at the corner of the tunnel.

It was the work of a few moments to undo the bolts at the four corners and lower the grille gently to the floor. Then Napoleon boosted Illya up into the hole overhead, tied a length of nylon rope from his pack around a corner of the grille and handed it up to his partner, who tucked the end in his teeth, leaving both hands free to pull him up into the air duct.

Together they hauled the grille back up from the floor, and used short lengths of rope to fasten it in place. A cursory examination from below would spot the change, but few people normally look over their heads, especially when bad air is blowing down upon them. Adding to this the dialogue they had heard outside, indicating that use of this passage was fairly uncommon, they felt reasonably secure in their jury-rigged arrangement.

Air-conditioning ducts are one of the most popular literary devices to enable the passage of persons, things and sounds from one point to another within a building, and as such have practically replaced the secret passages popular with another generation of novelists. But in actual practice, their very popularity has tended to defeat them. Most modern buildings include in their ventilating designs long verticals, baffles, internal grilles and occasional driving fans, all of which present moderate to severe problems for the casual tourist.

It was therefore a stroke of fortune that this particular installation had none of these internal protective devices. Napoleon didn't think to comment on it, feeling that his partner would share his conclusion that under the circumstances it was probably the Thrush builders had gone for efficiency rather than absolute safety. The island itself was certainly well enough protected, and the intake of the system was probably hidden quite well high above them on the mountainside. So there should have been no need for the usual security measures. And this was only reasonable—they couldn't have foreseen the positive brilliance of the U.N.C.L.E. technical staff and agents that had not only found the secret island base, but managed to evade all the other protective devices and carry the conflict home to the enemy.

Napoleon Solo was feeling perhaps a little too confident as he crept along the metal tunnel. There was a constant humming, a deep-pitched vibration that came to them through the steel walls and shook the air around them so gently it had to be listened for consciously. Somewhere machinery was working—probably an electrical generating plant.