"But…"

"In a few minutes, Jim." Dallen made the practised sideways movement of his jaw which switched off his transceiver, then tried to relax into the deep cushions of the seat. He felt a cold, pleasurable anticipation which — even though he could recognise it as a sickness — restored lost illusions of purpose.

The Valley was not really a valley. It was a narrow strip, almost a kilometre in length, where Orbitsvilles soil and bedrock had been scooped away to reveal a substantial area of shell material. Ylem was dark and non-reflective, so at night the strip had the appearance of a cold black lake. The research buildings anchored along it on suction foundations, continuously illuminated, looked like a flotilla of boats linked by power and communications cables.

Dan Cavendish had worked in the Valley for more than forty years, but he still got a contemplative pleasure from walking its length, knowing that only a few centimetres — the thickness of shell — beneath the soles of his boots was the edge, of interstellar space. Since the death of his wife three years earlier he had found it difficult to sleep the night through, and had developed the habit of patrolling the strip from end to end in the darkness, meditating and remembering. Although devoid of stars, the Orbitsville night sky had a beauty of its own which was conducive to an old man's evaluation of his life.

The popular conception of the Big O was of a thin shell of ylem, 320 million kilometres in diameter, completely englobing a small sun, but scientists were very much aware of a second concentric sphere without which the entire system would not have been viable. It was much smaller than Orbitsville and non-material in nature, a globular filigree of force fields capable of blocking the sun's outpourings of light and heat. It was composed of narrow strips, effectively opaque, whose function was to case great bars of shadow on the grasslands of Orbitsville, producing the alternating periods of light and darkness, day and night, necessary to the growth of vegetation. The inner sphere could not be stuthed directly, but its structure was observable in the bands of light and darkness moving across the far side of Orbitsville, roughly two astronomical units away. During a day period the banding showed as a delicate ribbed effect, barely noticeable, but at dusk the alternations of paler and deeper blue stood out vividly. And at night the hundreds of slim curving ribs became the dominant feature of the sky, swirling across it from two opposite points on the horizon, merging into a prismatic haze where they dipped behind denser levels of air.

Cavendish's life — all ninety-two years of it — had been spent on Orbitsville without his tiring of its beauty or its mystery. There were many questions about the incredible construct and he had refused to become dispirited over the fact that no answers had been forthcoming in spite of all the Optima Thule Science Commission's efforts. It was an article of his personal faith that a breakthrough was bound to come eventually, and if possible he wanted to be on hand when it happened. That was why he was dinging to his job in defiance of all efforts to make him retire. Now that Ruth was gone his work was all that was left to him, and he had no intention of giving it up for anybody. In particular, he was not going to be squeezed out by Phil Vigus, the senior technical manager, with whom he had been conducting a private feud for several years. The intrusive thought of Vigus caused him to snort with anger.

"Thinks I'm over the hill, does he?" Cavendish said to the encompassing darkness at the eastern end of the Valley. "I'll show the schmuck who's over the hill."

He unfolded his portable stool and sat down to rest, dismissing from his mind the stray thought that talking aloud to himself could be evidence that Vigus's claims were justified. It was a fine night, with just a few wisps of cloud drawn across the striated sapphire of the sky, and he had the place to himself. All other staff members had gone to their bungalow homes and the absence of lights on the slopes surrounding the Valley showed they were in bed and asleep. Cavendish repressed a pang of envy and regret as he recalled the deep comfort of waking in the darkness and staying awake just long enough to touch Ruth's shoulder and be reassured. They had had a good life together and he was not going to betray her at this stage by starting to feel sorry for himself. He took a deep breath, squared his shoulders and submerged his identity in the numinous magic of his surroundings, the glowing enigma that was Optima Thule at night.

So many unanswered questions…

Who had built Orbitsville? And why? Was it really an artefact, in the limited human sense of the word, or was it — as some religious thinkers maintained — evidence of a Creator who worked in diverse modes? Could it be a manifestation of Nature in a form which only seemed strange to men because of the paucity of their experience?

As a native of Orbitsville, Cavendish was instinctively inclined to the belief that it was a natural object, yet he had always been perplexed by certain salient features. There was, for example, the question of gravity. By means which no man could begin to understand, the thin shell of ylem generated gravity on the sphere's inner surface — and none on the outer surface — which suggested that Orbitsville had been designed as a habitat. There was also the matter of the portals. To a logical being there could be only one explanation for the three bands of circular apertures. They had to be entrances — but that led to the tricky concept of God as Engineer.

Some could accept that idea easily; others objected on the grounds that divine engineering should be divinely perfect, whereas there were unaccountable irregularities connected with the portals. Orbitsville itself was exactly spherical, a symmetry to satisfy any theologian, but why were there 207 portals on the equator instead of some number more suggestive of ethereal harmony? Why were the northern and southern bands not at precisely the same latitude, and why were there 173 portals in the former and only 168 in the latter? Furthermore, why did the portals themselves vary a little in size and spacing? The arguments had been raging for two centuries, with numerologists in particular mining their richest lode since the heyday of the Great Pyramid, but nothing was settled. Spherology continued with its record of non-achievement. Nobody understood why radio communications were impossible within the Big O. Nobody had analysed the mechanisms which kept the great shell in a stable relationship with the enclosed sun and its remote outer planet. Cavendish was an inorganic chemist and therefore was not professionally concerned with the problems of macro-spherology, but on the personal level he had his yearning for an advance, even a single step forward, to be made in the time that was left to him. It would compensate for the forty-plus years of frustration he had experienced since coming to the Valley.

His lean frame balanced uneasily on the stool, Cavendish gazed along the line of buildings floating on their lake of ink. Some had been stripped down and rebuilt several times as series of experiments were terminated and others took their places. A number of the buildings and machines had inverted counterparts of themselves, like mirror images, clinging to the outside of the Orbitsville shell and positioned by dead reckoning from the edge of the nearest portal. Although separated from each other by a mere eight centimetres of ylem, no machine had ever been able to communicate with its opposite number. Cavendish was usually positive in his outlook, but there were times when he suspected that his field of endeavour, shell structure, was the least promising in the Commission's programme.