Andy's blaster roared again. "Quick!" he barked, "Get inside the cave. It's our only chance...."
"This way," Frieda panted, the thin air of Io not providing enough oxygen for fast running.
Following her pointing finger, Andy saw a dark opening yawning in the face of the bluff. In other circumstances he would have instantly noticed that it had an artificial appearance, as if the cave had been cut into the stone by other than natural means. Frieda came to a panting halt just inside the entrance, but Oscar, his tail between his legs, skipped rapidly out of sight into the dark cavern. The thlot loved peace.
"Frieda—Miss Dahlem, I mean," Andy panted. "We're safe here, at any rate."
Almost immediately a blast shook the cavern. Loosened stone fell from the roof, there was a shower of debris outside, the cavern rumbled, and the light coming in through the entrance faded as a landslide almost completely blocked the opening.
"Hell!" Andy gasped, "another shot like that and we'll be buried alive. This is no place for us. Let's get out of here."
He moved to the entrance, his earth-sired muscles thrusting aside slabs of stone that he could not have handled on earth. Frieda worked with him. Together they cleared a space of less than two feet at the top of the cavern, which would allow them to slip out. Andy stuck his head out and immediately jerked it back.