The two bombs exploded almost simultaneously. The ground shook, and all over the cavern masses of stone came crashing to the floor. Bits of rock hummed and shrieked over our heads. And--yes! There was a draft of cooler, purer air on our faces. The bombs had done their work. "One more effort and we're outside, men," I called. "The passage is open, and there are only a few of the enemy before us. Ready?" "Ready!" went up the hoarse shout. "Then, forward!" It was easy to give the command, but hard to execute it. We were pressed so hard that only the men on the outside of the group could use their weapons. And our captors were making a terrible, desperate effort to hold us. Two more of our men were literally torn to pieces before my eyes, but I had the satisfaction of ripping holes in the heads of the creatures whose tentacles had done the beastly work. And in the meantime we were working our way slowly but surely to the entrance. * * * * * I glanced up as I dodged out into the open. That soft humming sound was familiar, and properly so. There, at an elevation of less than fifty feet, was the _Ertak_, with Hendricks standing in the exit, leaning forward at a perilous angle. "Ahoy the _Ertak_!" I hailed. "Descend at once!" "Right, sir!" Hendricks turned to relay the order, and, as the rest of the men burst forth from the cavern, the ship struck the ground before us. "All hands board ship!" I ordered. "Lively, now." As many years as I have commanded men, I have never seen an order obeyed with more alacrity. I was the last man to enter, and as I did so, I turned for a last glance at the enemy. They could not come through the small opening my bombs had driven in the rock, although they were working desperately to enlarge it. Leaping back and forth between me and the entrance I could see the vague, shadowy figures of the outside slaves, eagerly seeping up the life-giving fumes that escaped from the cavern. "Your orders, sir?" asked Hendricks anxiously; he was a very young officer, and he had been through a very trying experience. "Ascend five hundred feet, Mr. Hendricks," I said thoughtfully. "Directly over this spot. Then I'll take over. "It isn't often," I added, "that the Service concerns itself with economic conditions. This, however, is one of the exceptions." "Yes, sir," said Hendricks, for the very good reason, I suppose, that that was about all a third officer could say to his commander, under the circumstances. * * * * * "Five hundred feet, sir," said Hendricks. "Very well," I nodded, and pressed the attention signal of the non-commissioned officer in charge of the big forward ray projector. "Ott? Commander Hanson speaking. I have special orders for you." "Yes, sir!" "Direct your ray, narrowed to normal beam and at full intensity, on the spot directly below. Keep the ray motionless, and carry on until further orders. Is that clear?"