"Shut!" growled Hans. "The audiphone is on. The big adventure--and the commander--leaves me here just to watch!"

A slit in the observatory pane was open. The dark figure of one of the bandits on guard outside came and called softly up to us.

"Started. Hans?"

"Starting."

"Should it go wrong, call out."

"Yes. But it will not."

"There was an alarm, relayed probably to Great New York, the commander said, from Sp.a.w.n's garden. These cursed prisoners--"

"Shut! You keep watch out there. It is starting."

The guard slunk away. My attention went back to the mirror. An image was formed there now, coming from the eye of the lens upon De Boer's forehead. It swayed with his walking. He was evidently leading his men, for none of them were in the scene. The dark rocks were moving past. The lights of the mine were ahead and below, but coming nearer.

The audiphone hummed and crackled. And through it, De Boer's low-voiced command sounded:

"To the left is the better path. Keep working to the left."

The image of the rocks and the mine swung with a dizzying sweep as De Boer turned about. Then again he was creeping forward.

The mine lights came closer. De Beer's whispered voice said: "There they are!"

I could see the lights of the mine's guards flash on. A group of Sp.a.w.n's men gathered before the smelter building. The challenge sounded.

"Who are you? Stop!"

And De Boer's murmur: "That is correct, as Perona said. They expect us. Well," he ended with a sardonic laugh, "expect us."

His projector went up. He fired. In the silence of the control room we could hear the audiphoned hiss of it, and see the flash in the mirror-scene. He had fired into the air.

Again his low voice to his men: "Hold steady. They will run."

The group of figures at the smelter separated, waved and scattered back into the deeper shadows. Their hand-lights were extinguished, but the moonlight caught and showed them. They were running away; hiding in the crags. They fired a shot or two, high in the air.

De Boer was advancing swiftly now. The image swayed and shifted, raised and lowered rhythmically as he ran. And the dark shape of the smelter building loomed large as he neared it.

I felt Jetta beside me: heard her whisper: "Why, he should attack and then come back! Greko told my father--"

But De Boer was not coming back! He was dashing for the smelter entrance. Sp.a.w.n's guards must have known then that there was something wrong. Their shots hissed, still fired high, and our grid sounded their startled shouts. Then as De Boer momentarily turned his head, I saw what was taking place to the side of him. A detachment of the bandits had followed the retreating guards. The bandits' shots were levelled now. Dim stabs of light in the gloom. One of the guards screamed as he was struck.

The attack was real! But it was over in a moment. Sp.a.w.n's men, those who were not struck down, plunged away and vanished. Perona had disconnected the mine's electrical safeguards. The smelter door was sealed, but it gave before the blows of a metal bar two of De Boer's men were carrying.

In the unguarded, open strong-room, Perona, alone, was absorbed in his task of carrying the ingots of quicksilver down into the hidden compartment beneath its metal floor.

Our mirror was vague and dim now with a moving interior of the main smelter room as De Boer plunged through. At the strong-room entrance he paused, with his men crowding behind him. The figure of Perona showed in the vague light: he was stooping under the weight of one of the little ingots. Beside him yawned the small trap-opening leading downward.

He saw De Boer. He straightened, startled, and then shouted with a terrified Spanish oath. De Boer's projector was levelled: the huge, foreshortened muzzle of it blotted out half our image. It hissed its puff of light--a blinding flash on our mirror--in the midst of which the dark shape of Perona's body showed as it crumpled and fell. Like Sp.a.w.n, he met instant death.

Jetta was gripping me. "Why--" Gutierrez was with us. Hans was bending forward, watching the mirror. He muttered, "Got him!"

I saw a chance to escape, and pulled at Jetta. But at once Gutierrez stepped backward.

"Like him I will strike you dead!" he said.

No chance of escape. I had thought Gutierrez absorbed by the mirror, but he was not. I protested vehemently:

"I haven't moved, you fool. I have no intention of moving."

And now De Boer and his men were carrying up the ingots. A man for each bar. A confusion of blurred swaying shapes, and low-voiced, triumphant murmurs from our disc.

Then De Boer was outside the smelter house, and we saw a little queue of the bandits carrying the treasure up the defile. Coming back here to the flyer. There was no pursuit; the mine guards were gone.

The triumphant bandits would be here in a few moments.

"_Ave Maria, que magnifico!_" Gutierrez had retreated to our doorway, more alert than ever upon me and Jetta. Hans called through the window-slit:

"All is well, Franks!"

"Got it?"

"Yes! Make ready."

There was a stir outside as several of the bandits hastened down the defile to meet De Boer. And the tread of others, inside the flyer at their posts, preparing for hasty departure.

Hans snapped off the audiphone and mirror. He bent over his control panel. "All is well, Gutierrez. In a moment we start."

Through the observatory window I saw the line of De Boer's men coming: Abruptly Hans gave a cry. "Look!"

A glow was in the room. A faint aura of light. And our disconnected instruments were crackling, murmuring with interference. Eavesdropping waves were here! Hans realised it: so did I.

But there was no need for theory. From outside came shouts.

"Patrol-ship!"

"Hurry!"