Instantly up from that opening around our cylinders was rushing a torrent of air, a torrent of uprushing air that I understood well was caused by the warmer air beneath the roof rushing up into the colder outside atmosphere. But now down through that opening and through the air-currents the cylinders were swiftly dropping, and we could see far below in dim light a great compartment-city like the one we had found upon Neptune! In a moment more we would be below the roof, the opening closed above us, prisoned hopelessly in Triton to meet whatever fate our captors decreed. Already two of our four guards, and two of the Neptunians at the control-standard, had left the cylinder's upmost section and had clambered down the ladder to the lowest section in preparation for emerging. There was left with us in the upmost section of the cylinder only two guards and the Neptunian leader of the crimson-circle insignia at the control-standard. And as I saw that, I was leaning quietly toward Marlin. "Now's our chance, Marlin!" I whispered tensely. "If we could overpower these three Neptunians and the rest beneath afterward we might yet get back to Earth!" He glanced calmly around, then nodded. "We'll take it!" he whispered. "Once beneath this roof of Triton, there'll be no chance." "Go for the guard beside you, then, when I cough as signal," I told him. "If we can dispose of them and the leader there we can hold the rest below for a time." He met my eyes with his own, then turned and as though merely shifting a little in his seat moved nearer toward the guard on his side. I had already done the same toward the disk-bodied monster beside myself, both guards having slightly relaxed their first watchfulness. I glanced out, saw that even at that moment our cylinder was sinking with the others toward the great opening in the roof and knew that no moment was to be lost. So, with heart beating rapidly now, even as our cylinder prepared to sink down through the opening with the rest, I coughed slightly. In the next moment I had flung myself with a single motion upon the Neptunian guard beside me and had seen Marlin in the same instant throwing himself on the monster at his own side!