Robin became very excited when he heard this. It sounded to him as if somewhere up near the surface there must be an airtight cleft or bubble whose outer crust might be natural volcanic glass. Through this the sun might sometimes penetrate to produce the phenomenon Korree described.

Plainly then, this was the place Robin must find. It looked like the ideal place to begin his projected signaling to Earth. But whether it was or not, Robin would have to make a visit there to see.

Korree did not like the idea, but indicated he would be willing to go along. "Could you lead me there?" Robin asked.

"Much hard," Korree replied. "Can make do. You-me not like. Many-winter trip, many bubbles."

But Robin was determined. "We will go. First I must make a space suit. I may need it." Korree spread out a hand in acceptance.

It took about two months more to finish what Robin hoped would be a workable space suit. The helmet he finally managed to weld into something like a practical shape. It fitted over his head snugly, the little glass plate in front of his eyes. Its seams were closed as best as could be managed and sealed with melted animal fat. The bottom of the helmet fitted snugly over Robin's shoulders and would be attached to baggy leather arm-and-hand coverings. The bottom of Robin's body would be simply encased in several layers of clothing made as airtight as possible.

To carry a supply of air, Robin fashioned a large sack of Moonhound skins, which, when filled with air and brought to the surface of the Moon, would swell up like a huge balloon. He hoped that by breathing from this reserve he might be able to survive on the surface for perhaps twenty or thirty minutes. This would be all he would need, he estimated, to rush out, set up some sort of reflector or flare if he could contrive such, and dash back to safety. "Safety" would, of course, be some previously sealed dome extending to the surface, through which he could cut a space narrow enough to leave, and yet, one which would not be entirely exhausted of its inner gases by the time Robin got back to reseal it.

This was a long-chance project, yet it was the only hope Robin could think of. The matter could at least be examined at closer range if he could but find the cavern with the translucent roof. This would be an ideal base for his project.

Robin packed his equipment, liberated the last of his penned rabbits, and loaded as much food as he could in big sacks which he and Korree carried. Then, preceded again by Cheeky's monkey bounds, Robin turned his back on his "home" and headed back to the tunnel and the caverns beyond.

It had been over a year and a half since he had been cast away on the Moon, perhaps nearer two years. And now he was ready at long last to begin the long trek home.