Shep started to move into a better position to see when suddenly his foothold gave away beneath him. His cry blasted loudly over Rock’s receiver. Rock made an instinctive grab for his friend. He barely caught hold of an anchor ring on the other’s space belt in time to keep him from tumbling all the way to the ground. Rock steadied him as Shep thrust about with his feet for a new foothold. “I thought I was a goner!” Shep said tremulously. During the boys’ struggles they had evidently released loose material, for they saw a quantity of the porous stone cascade down the wall and strike the side of the ship. “We’ve got to scram!” Rock said urgently. “They’re bound to have heard that inside! Now they’ll know we’re on Luna!” They scrambled downward as fast as possible, without being reckless. It seemed as if the lunabase were more slippery than ever. Twice the boys’ feet slipped, and only timely bracing by the other prevented disaster. When they were about halfway down, Shep’s foot wedged into a crevice. “Look what I had to do with my big feet!” Shep groaned. “Don’t worry,” Rock said. “It’ll take them a few minutes to get space suits on if they have decided to come out and investigate.” Rock gently but firmly began working on his friend’s imprisoned foot. He moved it back and forth, tugging and pushing. But it held fast. Even after several minutes, Shep was still a prisoner. Then suddenly the thing that the boys had feared happened. The air lock of the _Dog Star_ opened and a ladder was thrust out until it reached the ground. Kalmus and two of his companions began descending. They all carried blasters. “Now we’re done—” Shep blurted, only to be shushed abruptly by his friend. Shep had forgotten that all the suit radios were on the same wave length. “I think we’re barking up the wrong tree!” the boys heard Ben Spooner say when they were on the ground. “That wasn’t anything but some loose rock that fell off that hill up there.” “Rocks don’t just fall on Luna!” Kalmus retorted. “Something has to move them! I still believe those guys have traced us here! Leo must have been able to contact them by radio before I could break up the set!” “I don’t see anybody around,” Mumbly Pegg remarked. “’Course you don’t see ’em!” Kalmus growled. “You dead brain! You don’t think they’re standing around waiting to be caught, do you? Start climbing up that hill, both of you!” Rock eased down as flat as he could get and motioned Shep to do the same. Through his helmet, Rock could see the grimace of pain on Shep’s face as his movement put pressure on the trapped foot. Rock cautioned him not to groan or speak a word. Over his radio Rock heard Spooner and Pegg breathing hard as they began scrambling up the formation, followed by Kalmus. Rock kept perfectly still, hoping with all his might that the men would not discover them. “I still think we’re barking up the wrong tree!” stocky Ben Spooner repeated as his breathing grew harder at every upward step.