It was into another long rectangular compartment that we passed, one that held, like that out of which we had just come, rows of strange many-cogged mechanisms. But one feature of that compartment caught our attention instantly, held us motionless and staring. And that was that those rows of great mechanisms were not complete! Here and there in those rows were gaps, as though machines had been removed from the compartment, and where those gaps were, where the missing machines had stood, were squares on the floor where their bases had rested, _squares that were entirely free of the inch-thick dust that lay over all else_! And even as we stared, as we comprehended the astounding significance of that, we saw that upon the dust-coated floor before us were many tracks, small round and strange tracks in the thick dust that were of great number and that had been made, it was apparent from their dust-free condition, but days or hours before! "Marlin!" I whispered, grasping my companion's space-walker with the great metal arm of my own and touching head casing to head casing. "Marlin--those tracks--someone, something has been here--and but recently!" "It can't be!" he exclaimed, his voice hushed strangely like my own. "Neptune--all this great compartment-city--it's all dead, deserted----" "But those tracks!" I insisted. "Those squares in the dust--something's been here and has taken a half-dozen of these great machines away with them! And we know that something on Neptune is sending the great force-ray out to the sun!" "It can't be," Marlin repeated. "We found no source of the great ray on Neptune's sunward side, and, too, how can that ray shoot always toward the sun from some spot on Neptune when Neptune itself is constantly turning? No, Hunt, I think that this means--_but look up there_!" As he cried out he was gazing suddenly upward, his space-walker's great arms pointing up, and at that horror-stricken cry, I glanced up to see a sight that froze me motionless there in astonishment. For there, high above us and above the great compartment-city, a dozen strange great shapes were dropping down through the air toward us, were dropping down through one of the openings in the great roof! Long great cylinders of gleaming metal those shapes seemed, dropping silently and smoothly down from the opening, toward the compartment-city, but even as we looked in amazement and terror up toward them, they had halted in mid-air, as though seeing the faceted ball of our hovering space-flier hanging above the city far behind us. Then the next instant all the dozen great cylinders were flashing with unbelievable speed toward our space-flier, a half-score narrow, pencil-like rays of pale, almost invisible light or force stabbing ahead of them toward the space-flier!