"Wow, what a leak!" Darl started forward. "How's it below, in the mine?"

"Normal. It's the Dome air that's going!"

"Shoot on the smoke and I'll spot the hole. Quick, man!"

"Okay!"

Thomas' long legs shot him out of the headquarters tent. Just beyond the entrance flap was one of the two gyrocopters used for flying within the Dome. He leaped into the cockpit and drove home the starter-piston. The flier buzzed straight up, shooting for the misted roof.

The Earthman fought to steady his craft against the hurricane wind, while his gray eyes swept the three-mile circle of the vault's base. He paled as he noted the fierce speed with which the white smoke-jets were being torn from the pipe provided for just such emergencies. His glance followed the terrific rush of the vapor. Big as a man's head, a hole glared high up on the Dome's inner surface. Feathered wisps of tell-tale vapor whisked through it at blurring speed.