Thorn rapidly prepared for their precarious stratagem. There were six holes around the perimeter of the drain from which the deadly, invisible beams emerged. He took the six most regularly-shaped of his slith-teeth, and laid them in readiness.
Then with the end of his lamp, Thorn swiftly pushed the teeth into place. As each big white tooth was shoved forward, it became a conical plug to close the beam-aperture. By the time the sixth tooth was tamped into place, the first one was already charring and smelling.
"Come on!” Thorn cried, and plunged forward in a scrambling leap through the teeth-plugged circle of holes.
Sual Av followed instantly, the Venusian's wigged head butting into Thorn's back. A moment later, Gunner Welk caromed into the Venusian from behind with battering force.
"Jacket's on fire!” gasped the Mercurian, beating at his side. A smell of scorched cloth filled the dank air.
There was a frantic squirming in the cramped tunnel as the other two Planeteers tried to help Gunner beat out his smoldering jacket. He and Sual Av soon had it extinguished.
"Are you hurt, Gunner?” Thorn asked anxiously.
"No, just my side scorched a little,” panted the Mercurian. “One of those teeth burned clear out just as I jumped. It's lucky it was one slith instead of in the middle!"
Thorn glanced back past them. The slith-teeth with which he had plugged the apertures had vanished. Even that super-hard substance had been charred away in a few seconds by the beams.
"Let's get on,” growled the Mercurian in a moment. “These damned drains aren't exactly a pleasure resort."
Again Thorn started forward on hands and knees, lighting the way with his red beam. He moved with extreme caution, alert to detect the presence of another invisible, deadly web.
But they met no more such barriers. Presently they reached a place where the drain forked into five smaller tubes.
"Which one?” whispered Sual Av to him.
"We'll each take one, trace it and come back and meet here,” Thorn muttered. “One of them ought to lead to the dungeons."
Thorn crawled into the right drain tube. It was so small he had to inch forward by creeping. It slanted upward also.
Blue light finally glimmered ahead. Thorn extinguished his lamp and stealthily crawled on. He came to the end of the drain, which was closed by inertrum bars set in the cement, over his head.
Cautiously he peered upward. The grating over him was set in the cement paving of a large court surrounded on all sides by the dark, towering mass of the citadel. Krypton lamps cast a blue glow on spaceships parked in the court, three swift-lined small cruisers. Two armed guards paced to and fro beside them.
"Haskell Trask's personal spacecruisers,” Thorn muttered to himself.
He backed down to the fork where the drains diverged. Gunner Welk and Sual Av were just emerging there also.
"The dungeons are up there at the end of that pipe!” Sual Av whispered excitedly, pointing to the second drain.
"Come on, then,” Thorn said swiftly.
He led the way, all three of them crawling up the narrow pipe the Venusian had explored. Its opening, also, was barred by inertrum bars set in the cement.
Thorn peered up through the bars into a short blue-lit corridor, along whose walls were the inertrum doors of cells. Almost all of the cells seemed unoccupied, their doors half-open. No prisoner stayed long in Haskell Trask's dreaded private dungeon!
"It's Trask's dungeon, all right,” Thorn whispered. “And no guards in sight. Go back down the pipe a little."
The other two Planeteers obeyed, all three backing down the tube a little way. Thorn drew his pistol, sighted carefully at the grating above, and pulled the trigger.
The little atom-shell exploded in a small, brilliant flare of atomic energy, with a thudding reverberation. The flare burned away a mass of cement at one side of the grating, completely exposing the ends of the imbedded inertrum bars.
Thorn clambered eagerly up to the grating at once. At the same moment he heard a cry of alarm from up in the corridor. Two Saturnian guards came rushing out of one of the cells, dropping a flask of fungus wine they had been secretly drinking, and drawing their atom-pistols. The thud of the atom-shell had roused them.
They saw Thorn's head below the grating and fired at him instantly. Their shells struck the floor in front of the grating and a flare of blinding light and scorching heat hit Thorn's face. He fired his own atom-pistol, triggering quickly. More flares of energy burst brilliantly beside the two Saturnian guards, down the corridor.
The two green-faced soldiers crumpled and lay still, in a scorched and lifeless heap. Thorn waited, his face wild in the pale blue light, gripping his weapon. But the swift thudding of the shells was not followed by any further alarm.
"Those must be the only guards on duty. inside the dungeon,” Thom panted, tearing away the freed inertrum bars with quivering hands.
The Planeteers scrambled hastily up out of the drain into the short single corridor of the dungeon.
"Listen! I hear someone!” Sual Av exclaimed.
Then the other two comrades heard. It was a voice from the farther end of the corridor, a distant, monotonous, strangely metallic voice speaking on and on.
"Erebus — won't think of Erebus — think of anything but Erebus — won't think of Erebus—"
Thorn started wildly. “Erebus? That must be Lana talking! Come on!"
"It didn't sound like a human voice,” Gunner muttered, as he and the Venusian raced after Thorn.
They leaped over the scorched bodies of the dead Saturnians, and on down the corridor. The voice came from the last cell in the passage. Now they heard it more clearly, and it was not a human voice. It spoke in cold, metallic, inflectionless tones, on and on without stopping.
"I mustn't think of Erebus — mustn't think of the secret! Keep my mind on something else—"
Thorn reached the door of that last cell. He peered through the little grating in the inertrum door. And his brown face froze, his eyes widened wildly, at what he saw.
"Good God, it's Lana!” he whispered hoarsely. “They've got a psychophone attached to her!"
The cell into which Thorn wildly gazed was a windowless cubicle, lit by a single krypton lamp in the ceiling. Under the uncanny blue glow, in a metal chair to which her arms and legs were tightly strapped, sat Lana Cain. The girl's slender little figure was sagging in her bonds, her eyes were closed, her white face infinitely weary and exhausted. It was not Lana who was speaking, but the complex machine that was attached to her head.
Tiny, needlelike incisions had been made in the base of Lana's skull. From them, two thin black wires ran upward to the mechanism suspended above her, a compact complexity of transformers and vacuum tubes, upon which was mounted an audio-speaker.
The metallic, monotonous voice came from that audio-speaker. It was still speaking steadily on, and everything it said was being taken down upon the moving tape of a recorder whose microphone hung in front of the speaker.
"Think of something else,” the metallic voice came from the speaker as the Planeteers listened. “Think of the Zone — of Stilicho — of my father—"
"A psychophone!” repeated Sual Av, wide-eyed. “So that's how Trask is trying to get the secret of Erebus from Lana!"
Thorn too was thunderstruck by the ingenuity of the means being used to secure the girl's secret knowledge.
The psychophone was a mechanism that made thought audible. Once it was connected to a subject's nerve centers, every conscious thought in that subject's brain was translated into mechanical speech by the machine and spoken aloud. That was accomplished by transmitting the tiny electrical neural currents of the subject's thought-impulses into a complex scanner, in which the particular vibration of each thought actuated the nearest word or phrase that expressed that thought, in the phono-recorded vocabulary of the thing.