Miss Kanton flushed and turned away towards the Central Tower. The other three caught up with her and four abreast they walked lightly over the rough plain. Through the thin atmosphere and over the helmet phones they heard the crashing drone of the mine in operation. To the Tindars it did not sound right. There was too much noise. The robot-diggers and refiners were supposedly working far below the ground. Ahead of them, over the close horizon, sprang a great, looming metal shape that filled the air with the roar of its engines. It rushed towards them with a flat, toothed platform lowered slightly into the ground. The platform was nearly twenty feet in length, with a thousand metal claws above it hungrily scooping the soil up into the black maw of the storage bin that swelled from it like a monstrous belly. "It's a digger!" Alpha cried. "Get out of the way!" In the weak gravity they were able to move by bounds out of the path of the mining machine. It roared past them, tearing up the ground in a dumb frenzy. "The ships!" Miss Kanton shouted, screaming above the roar of the Digger. [Illustration: _"There goes our ship!" Kay screamed._] "Too late!" Beta gasped. "It has one!" There was a crashing clank and the cry of twisted steel as the machine grabbed the small rocket ship up and crushed it in its jaws. The ship vanished into the bulging bin that followed the mouth on swiftly spinning wheels. The digger growled over the other horizon, leaving in its wake a shallow, wide furrow. "I'll get the other ship to safety!" Alpha cried and ran towards it. "What are the Diggers doing on the surface?" Miss Kanton asked Beta. "They're supposed to be underground." "Something is all wrong," Beta said. "The Controls are obviously scrambled. Radio guides the diggers, keeps them underground until they're full, then lets them come up to empty." "Do you think you can fix it?" Miss Kanton's dupe asked. "If it's external trouble, yes," Beta said. "But if it's inside the seals, we'd never be able to get at it. Everything is sealed against tampering. The controls are in vaults. How they ever got scrambled, I can't imagine." "No wonder there weren't any radio reports," Miss Kanton said. "This place is a madhouse! Look, here comes another one!" Another Digger appeared on the horizon but it was far to one side, a moving shape against the stars. "We'd better get into the control tower," Beta said. "It's probably the only safe place on this rock." They were illuminated momentarily by the blasting jet of the ship as it arced upwards from the uneven ground. As they hurried towards the tower, the ship blasted past them and whistled to a halt near the door of the tower.