Echo is naturally magnetic, probably more so than any other planetoid—and Neal Bormon cursed softly, just to relieve his feelings, as that magnetism gripped the small iron plates on the soles of the rough boots with which the Martians had provided him. Slavery—and in the twenty-ninth century! It was difficult to conceive of it, but it was all too painfully true. His hands, inside their air-tight gauntlets, wadded into fists; little knots of muscle bulged along his lean jaw, and he stared at the darkness around him as if realizing it for the first time. This gang had plenty of guts, to shanghai men from the Earth-Mars Transport Lines. They'd never get by with it.

And yet, they had—until now. First, Keith Calbur, and then himself. Of course, there had been others before Calbur, but not personal friends of Neal Bormon. Men just disappeared. And you could do that in the Martian spaceport of Quessel without arousing much comment—unless you were a high official. But when Calbur failed to show up in time for a return voyage to Earth, Bormon had taken up the search.

Vague clews had led him into that pleasure palace in Quessel—a joint frequented alike by human beings and Martians—a fantasmagoria of tinkling soul-lights; gossamer arms of frozen music that set your senses reeling when they floated near you; lyric forms that lived and danced and died like thoughts. Then someone had crushed a bead of reverie-gas, probably held in a Martian tentacle, under Bormon's nostrils, and now—here he was on Echo.

He gave an angry yank at the chain which was locked around his left wrist. The other end was fastened to a large metal basket partly filled with lumps of whitish-gray ore, and the basket bobbed and scraped along behind him as he advanced. Of the hundred or more Earthmen, prisoners here on Echo, only seven or eight were within sight of Bormon, visible as mere crawling spots of light; but he knew that each was provided with a basket and rock-pick similar to his own. As yet he had not identified anyone of them as Keith Calbur. Suddenly the metallic voice of a Martian guard sounded in Bormon's ears.

"Attention. One-seven-two. Your basket is not yet half filled, your oxygen tank is nearly empty. You will receive no more food or oxygen until you deliver your quota of ore. Get busy."

"To hell with you!" fumed Bormon—quite vainly, as he well knew, for the helmet of his space suit was not provided with voice-sending equipment. Nevertheless, after a swift glance at the oxygen gauge, he began to swing his rock-pick with renewed vigor, pausing now and then to toss the loosened lumps of ore into the latticed basket. On Earth, that huge container, filled with ore, would have weighed over a ton; here on Echo its weight was only a few pounds.

Neal Bormon had the average spaceman's dread of oxygen shortage. And so, working steadily, he at last had the huge basket filled with ore—almost pure rhodium—judging by the color and weight of the lumps. Nearby, a jagged gash of light on the almost black shoulder of Echo indicated the location of that tremendous chasm which cut two-thirds of the way through the small asteroid, and in which the Martians had installed their machine for consuming ore.

Locating this gash of light, Bormon set out toward it, dragging the basket of ore behind him over the rough, rocky surface.

The ultimate purpose of that gargantuan mechanism, and why this side of the planetoid apparently never turned toward the sun, were mysteries with which his mind struggled but could not fathom.

Presently, having reached the rim of the abyss, with only a narrow margin of oxygen left, he commenced the downward passage, his iron-shod boots clinging to the vertical wall of metallic rock, and as he advanced this magnetic attraction became ever more intense. The blaze of lights before him grew brighter and seemed to expand. Dimly, two hundred yards over his head, he could glimpse the opposite wall of the chasm like the opposing ja