Behind them they could hear a crashing and every now and then a shouted word. Robin wondered what was being said, but Peter, sensing his wonder, gasped out, "He's shouting ... the word for devils! When ... he came to ... he believed himself ... in some sort ... of Troll kingdom ... with me ... as a ... devil." "Crazy! Stark raving mad!" shouted Robin back. On they went. The helmet banging against Robin's back made him feel clumsy and odd, yet he moved through the air with the agility of a phantom. Now, suddenly, there loomed a dark wall before them and they caught themselves back just in time to keep from smashing headlong into it. "The wall!" shouted Robin. Peter pulled his arm, started hurrying along to one side. He gave a sharp cry of relief, pulled Robin to him. "Here we are, the ledge. Go on up!" Peter started off. Robin followed as fast as was possible. There was evidently a thin ledge running up the side of the cave. In places it was a gentle slope angling upward, in other parts there was a sudden step. In their haste there was no time to pick and choose their steps. Several times Robin tripped, almost falling, but he had built up such a momentum that he simply slammed and banged over the obstacles, charging up the ledge with a luck and agility that would have made a mountain goat jealous. Behind them, at the base of the cliff, they now heard Von Borck's roaring. "_Teufel!_" he was calling. Then suddenly from where the madman stood, there beamed out a flash of yellow light. A flashlight, thought Robin, he had a flash. The beam passed rapidly over the cave wall seeking the escapers. Once or twice they froze against the side as it passed over them, dashing on as soon as it was gone. Then Von Borck's light caught them, held them. "Keep running," yelled Peter, "it's not far now!" The two kept up. Then there was a sharp report below them and something went _spang_ on the rock wall near Robin. A bullet ... the mad rocket pilot was firing at them. Now they simply raced on, ignoring the German's wild shots. "Here we are!" gasped Peter and seemed to melt right into the cliff face. Robin saw the black opening in the next second and tumbled into it, to be caught by his brother's arms. For an instant they stood there in the darkness, catching their breath. Then a light appeared in Peter's hand, and Robin saw that he held an electric torch there, part of his space-suit equipment. The beam illuminated a narrow, dark tunnel leading steeply upward apparently through the solid rock. "This way!" said Peter and started off. Robin followed him on into the narrow path that would lead him at long last to the surface of the Moon. _16. On the Crater Floor_ The tunnel was very narrow, a mere crack in the wall, and Robin was hard put to squeeze through in a couple of spots. But it was not too long and, in a few minutes, Robin felt from the change in air and echo that it had opened out into a wider area.