Wearied and worn out as they were, they hurried forward, and abruptly there was something which impeded their movements. They could reach their hands into the impalpable barrier. For one foot, two, or even three. But an intolerable pressure thrust them back. Thorn seized a sapling and ran at the barrier as if with a spear. It went five feet into the invisible resistance and stopped, shot back out as if flung back by a jet of compressed air. "He told the truth," groaned Thorn. "We can't get out!" * * * * * Long shadows were already reaching out from the mountains. Darkness began to creep upward among the valleys. Far, far away a compact dark cloud appeared, a combat-squadron. It swept toward the dome and dissociated into a myriad specks which were aircraft. The fliers already swirling about the invisible dome drew aside to leave a quadrant clear, and Combat-Squadron Seven merged with the rest, making the pattern of dancing specks markedly denser. "With a fire," said Thorn desperately, "they'll come! Of course! But Kreynborg took my lighter!" Sylva said hopefully: "Don't you know some way? Rubbing sticks together?" "I don't," admitted Thorn grimly, "but I've got to try to invent one. While I'm at it, you watch for fliers." He searched for dry wood. He rubbed sticks together. They grew warm, but not enough to smoke, much less to catch. He muttered, "A drill, that's the idea. All the friction in one spot." He tugged at the ring under his lapel and the parachute fastened into his uniform collar shot out in a billowing mass of gossamer silk, flung out by the powerful elastics designed to make its opening certain. Savagely, he tore at the shrouds and had a stout cord. He made a drill and revolved it as fast as he could with the cord.... A second dark cloud swept forward in the gathering dusk and merged into the mass of fliers about the dome. Five minutes later, a third. Dense as the air-traffic was, riding-lights were necessary. They began to appear in the deepening twilight. It seemed as if all the sky were alight with fireflies, whirling and swirling and fluttering here and there. But then the fire-drill began to emit a tiny wisp of smoke. Thorn worked furiously. Then a tiny flickering flame appeared, which he nursed with a desperate solicitude. Then a larger flame. Then a roaring blaze! It could not be missed! A fire within the dome could not fail to be noted and examined instantly! * * * * * A searchlight beam fell upon them, illuminating him in a pitiless glare. Thorn waved his arms frantically. He had nothing with which to signal save his body. He flung his arms wide, and up, and wide again, in an improvised adaption of the telegraphic alphabet to gesticulation. He sent the watch call over and over again....