with our Earth motor. There is very little radiactum available on Mars, and our government will not allow our own supply to be exported. What do you suppose that company on Mars would pay for a few tons of richly radioactive radiactum such as Grantline may have found on the Moon?"
"But," I objected, "That is a reputable Martian company. It's backed by the government of the Martian Union. The government of Mars would not dare—"
"Of course not!" Captain Carter exclaimed sardonically. "Not openly! But if Martian Brigands had a supply of radiactum I don't imagine where it came from would make much difference. The Martian company would buy it, and you know that as well as I do!"
Halsey added, "And George Prince, my agents inform me, seems to know that Grantline is on the Moon. Put it all together, lads. Little sparks show the hidden current.
"More than that: George Prince knows that we have arranged to have the Planetara stop at the Moon and bring back Grantline's ore.... This is your last voyage this year. You'll hear from Grantline this time, we're convinced. He'll probably give you the signal as you pass the Moon on your way out. Coming back, you'll stop at the Moon and transport whatever radiactum ore Grantline has ready. The Grantline Flyer is too small for ore transportation."
Halsey's voice turned grimly sarcastic. "Doesn't it seem queer that George Prince and a few of his Martian friends happen to be listed as passengers for this voyage?"
In the silence that followed, Snap and I regarded each other. Halsey added abruptly:
"We had George Prince typed that time we arrested him four years ago. I'll show him to you."
He snapped open an alcove, and said to his waiting attendant "Flash on the type of George Prince."
Almost at once, the image glowed on the grids before us. He stood smiling sourly before us as he repeated the official formula:
"My name is George Prince. I was born in Greater New York twenty-five years ago."
I gazed at this televised image of George Prince. He stood somber in the black detention uniform, silhouetted sharply against the regulation backdrop of vivid scarlet. A dark, almost femininely handsome fellow, well below medium height—the rod checking him showed five foot four inches. Slim and slight. Long, wavy black hair, falling about his ears. A pale, clean-cut, really handsome face, almost beardless. I regarded it closely. A face that would have been beautiful without its masculine touch of heavy black brows and firmly set jaw. His voice as he spoke was low and soft; but at the end, with the concluding words, "I am innocent!" it flashed into strong masculinity. His eyes, shaded with long girlish black lashes, by chance met mine. "I am innocent." His curving sensuous lips drew down into a grim sneer....
Halsey snapped a button. He turned back to Snap and me as his attendant drew the curtain, hiding the black grid.
"Well, there he is. We have nothing tangible against him now. But I'll say this: he's a clever fellow, one to be afraid of. I would not blare it from the newscasters' stadium, but if he is hatching any plot, he has been too clever for my agents!"
We talked for another half-hour, and then Captain Carter dismissed us. We left Halsey's office with Carter's final words ringing in our ears. "Whatever comes, lads, remember I trust you...."
* * * * *
Snap and I decided to walk part of the way back to the ship. It was barely more than a mile through this subterranean corridor to where we could get the vertical lift direct to the landing stage.
We started off on the lower level. Once outside the insulation of Halsey's office we did not dare talk of this thing. Not only electrical ears, but every possible eavesdropping device might be upon us. The corridor was two hundred feet or more below the ground level. At this hour of the night the business section was comparatively deserted. The stores and office arcades were all closed.
Our footfall echoed on the metal grids as we hurried along. I felt depressed and oppressed. As though prying eyes were upon me. We walked for a time in silence, each of us busy with memory of what had transpired at Halsey's office.
Suddenly Snap gripped me. "What's that?"
"Where?" I whispered.
We stopped at a corner. An entryway was here. Snap pulled me into it. I could feel him quivering with excitement.
"What is it?" I demanded in a whisper.
"We're being followed. Did you hear anything?"
"No!" Yet I thought now that I could hear something. Vague footfalls. A rustling. And a microscopic whine, as though some device were within range of us.
Snap was fumbling in his pocket. "Wait! I've got a pair of low-scale detectors."
He put the little grids against his ears. I could hear the sharp intake of his breath. Then he seized me, pulled me down to the metal floor of the entryway.
"Back, Gregg! Get back!" I could barely hear his whisper. We crouched as far back into the doorway as we could get. I was armed. My official permit for the carrying of the pencil heat ray allowed me always to have it with me. I drew it now. But there was nothing to shoot at. I felt Snap clamping the grids on my ears. And now I heard something! An intensification of the vague footsteps I had thought I heard before.
There was something following us! Something out in the corridor there now! The corridor was dim, but plainly visible, and as far as I could see it was empty. But there was something there. Something invisible! I could hear it moving. Creeping toward us. I pulled the grids off my ears.
Snap murmured, "You've got a local phone?"
"Yes. I'll get them to give us the street glare!"
I pressed the danger signal, giving our location to the operator. In a second we got the light. The street in all this neighborhood burst into a brilliant actinic glare. The thing menacing us was revealed! A figure in a black cloak, crouching thirty feet away across the corridor.
Snap was unarmed but he flung his hands out menacingly. The figure, which may perhaps not have been aware of our city safeguard, was taken wholly by surprise. A human figure, seven feet tall at the least, and therefore, I judged, a Martian man. The black cloak covered his head. He took a step toward us, hesitated, and then turned in confusion.
Snap's shrill voice was bringing help. The whine of a street guard's alarm whistle nearby sounded. The figure was making off! My pencil ray was in my hand and I pressed its switch. The tiny heat ray stabbed through the air, but I missed. The figure stumbled but did not fall. I saw a bare gray arm come from the cloak, flung up to maintain its balance. Or perhaps my pencil ray had seared his arm. The gray-skinned arm of a Martian.
Snap was shouting, "Give him another!" But the figure passed beyond the actinic glare and vanished.
We were detained in the turmoil of the corridor for ten minutes or more with official explanations. Then a message from Halsey released us. The Martian who had been following us in his invisible cloak was never caught.
We escaped from the crowd at last and made our way back to the Planetara, where the passengers were already assembling for the outward Martian voyage.
CHAPTER II.
I stood on the turret balcony of the Planetara with Captain Carter and Dr. Frank, the ship surgeon, watching the arriving passengers. It was close to the zero hour; the level of the stage was a turmoil of confusion. The escalators, with the last of the freight aboard, were folded back. But the stage was jammed with incoming passenger luggage, the interplanetary customs and tax officials with their x-ray and zed-ray paraphernalia and the passengers themselves, lined up for the export inspection.
At this height, the city lights lay spread in a glare of blue and yellow beneath us. The individual local planes came dropping like birds to our stage. Thirty-eight passengers to Mars for this voyage, but that accursed desire of