As Ed and Barbara plodded on through the day, their minds became fuzzy with weariness. Once, in a kind of retreat from present harsh facts, Ed's thoughts touched a vivid daydream that he'd had before, of a planet of some star. He looked down at imaginary dry ground under imaginary feet and saw that each pebble under the strange, brilliant sunshine had a little hole in it. And something shaped like a cross, with four rough, brownish-gray arms that could bend in any direction, scrabbled away, flat against the soil, its equipment glinting. The thickets all around were stranger than those of Mars. Yes, it was just a daydream, originating from within himself, like an old, half-buried hope of some distant exploration. He wondered if it could ever still have any fulfillment, or if that even mattered any more? Perhaps, for all he knew, his wife and he were now headed for an even stranger region. Ed shook his head to clear it. He did not want to disturb the envelope in his pouch too often. To expose the ink to the dried-out Martian air, while the writing was in progress at hour-hand speed, might spoil a vital message. But at last he chanced it. It seemed that the writer was not much troubled by the presence of the bird-thing or what it might mean. Barbara and Ed read avidly: "_Base of capped granite rock before you. Lab._" Barbara nodded toward a formation which loomed a half mile ahead in the freezing cold of late afternoon. The slab, balanced crosswise on a slender pinnacle, identified it beyond doubt, though there were other similar spires around it. It cast its shadow on the sunlit dunes. Or was all of that dark, irregular patch shadow? Ed Dukas and his bride had not enjoyed the luxury of natural sleep for a long time. But summoning their flagging strength, they hurried forward. Ed felt that at last he was approaching the solution of ten-year-old enigmas. The darker area at one side of the capped rock was not all shadow. But the Dukases had scant attention for the bluish masses of plushy stuff that grew in this aridity. At another time it might have been fascinating, for it was vegetation related to the android as moss is related to a man. It was a growth of vitaplasm--another of Mitchell Prell's experiments. But Ed and Barbara had no chance to ponder this. They located an eighteen-inch cleft at the rock's base. Edging into it, they found an irregular stone pivoted on steel hinges. To their touch, it closed behind them, and bolts clicked. From the outside now the outline of the door would seem merely a pattern of natural cracks in the granite pinnacle. Atomic battery lamps lighted the passage, and there were more heavy doors, some of them of steel, for Ed and Barbara to bolt behind them. The place was like a small, secret fortress. At the bottom of a spiral stair, beyond a small airlock, was Mitchell Prell's latest and perhaps last workshop.