Jean hit the button with the heel of her right hand. There was an explosion, a wrenching jolt and a second later she was adrift in space, only fifty kilometres above the inconceivable vastness of Orbitsville.

Jean's first reflexive action was to check that the capsule's radio beacon was functioning properly. She located the pulsing green rectangle on the miniature instrument panel, touched it for reassurance, then raised her eyes to see how the doomed freighter was faring. The coffin-sized capsule had all-round visibility, and from its viewpoint the universe was divided into two equal parts. "Above" was a hemisphere of stars, many of them individually brilliant against fainter swarms and the frozen luminous clouds of the Milky Way; "below" there appeared to be nothing.

In spite of her years of plying the two-hundred-plus equatorial portals, Jean's brain still tended to interpret the scene as though she were in a low-flying plane which was skimming the surface of a dark ocean. She scanned the region directly below the capsule, expecting to pick out the lights of the freighter at once, and was surprised and only faintly alarmed to observe unbroken night. Did it mean that every power source on the ship had failed, dousing even the astrogation lights?

That can't be, she told herself. Not so soon.

She frowned, still puzzled rather than worried, turning her head from side to side to take in larger areas of the blackness below her. Then, from a corner of her eye, she became aware of something huge occulting the star fields above her. She twisted around in the confined space and verified what the first intuitive shock had already told her — that the opaque mass was the freighter sliding ahead on its own course.

Refusing to allow herself to panic, Jean studied the larger vessel and tried to decide what had gone wrong with the escape. The answer came quickly. Astrogation and marker lights were slipping across the long silhouette at increasing speed, which meant that the dysfunction of its thrust controllers had caused the ship to rotate. And instead of the capsule having been ejected upwards, to carry it into space and clear of the equatorial trade lanes, it had been fired downwards in the direction of Orbitsville. She was bound for a grazing collision with the unseen surface a mere fifty kilometres below.

Until that moment Jean's principal concern had been the loss of the Atkinson Grimshaw, the old ship — named after a favourite Victorian artist — which was on the point of annihilating both itself and most of her assets. With the skimpiness of her insurance coverage, the incident probably meant the end of the one-woman transport business she had been operating for eight years, ever since her mother had died, but now such considerations were trivial. The capsule was travelling downwards at about forty kilometres an hour, and also had a forward component of about thirty thousand — the speed at which it had parted company with the ship. These velocities, relative to the Orbitsville shell, were small compared to normal operational speeds, but they were enough to destroy the thin-walled capsule in the collision which was due in approximately seventy-five minutes.

Life or death, for her, had become a question of how long it would take the rescue services to react.

At the age of forty, Jean had retained the instinctive belief in immortality which comes from good health, good looks, an active intelligence and a satisfying life style. But now, floating in silence above the invisible vastness of the Big O's outer surface, she had to weigh up the chances of surviving the day, knowing in advance that the odds were not in her favour.

Orbitsville had three bands of circular portals — one at its equator, one in each of the northern and southern hemispheres. Those on the equator, spaced at intervals of roughly five-million kilometres, had been given the identification numbers 1 to 207, counting east from the portal which had first been penetrated by Vance Garamond and the crew of his SEA flickerwing. Thriving ports and cities had subsequently sprung up around many of the entrances during the great migrations from Earth, and at that time the equatorial trade lanes had been busy and well regulated. But those cities had been built almost from force of habit, dying manifestations of mankind's need for safe huddling places. With unlimited territory available there was no longer any need for competition, conflict or defence. The millions from Earth had been effortlessly absorbed, lured by Orbitsville's endless savannahs, and — as quickly as they were created — many cities had been abandoned, echoing the fate of their forebears on the home world.

During Jean's career the interportal space traffic had dwindled drastically, and therein lay the threat to her life. She had been flying east from 156 to another still-viable industrial centre at 183. Eighty minutes into the flight she was, as a consequence of me freighter's puny acceleration, only twenty-thousand kilometres from her starting point, and in the old days would quickly have been reached by the high-performance patrol vessels monitoring the traffic around each portal. In the last decade of the 23rd Century, however, the emergency services had been pared down to the minimum and in any case were accustomed to the leisurely type of recovery mission which would have been effective had Jean been ejected upwards. She had a conviction that nobody would even notice anything unusual about her distress signal until it was too late.

She stared down into the featureless blackness and tried to see it as an incredibly hard wall which was rushing upwards with deadly speed. The air circulating around her smelled strongly of rubber and plastics, a reminder that the capsule was new, having been installed a year earlier in compliance with safety regulations. She almost smiled at the irony involved. The old capsule had been equipped with full radio communication and a Covell propulsion unit — either of which could have been enough in her present circumstance to make the difference between living and dying.

Brave new world! Another indication that humans bad turned their hacks on spate travel, that the dispersal of whole cultures could he followed by pointing telescopes into the night skies of the Big O interior, charting the firefly glows of their caravans and camps…

As the minutes went by Jean's fear increased. A normal reaction would have been to scan the band of sky close to the Orbitsville horizon in the hope of seeing marker lights drawing near, but she was unable to drag her gaze from the spurious depths below. How far away was the shell now? Could the altimeter have been as haywire as everything else on the Atkinson Grimshaw, giving an inflated reading? Would the capsule's flashing beacons produce even the faintest smudge of reflection in the instant before the collision? Mesmerised, unblinking, Jean stared into the crawling darkness, trying to penetrate screens of after-images to reach the terrible reality beyond.

She had been that way for some time, her lips drawn into a unconscious grimace, when wonder intervened.

First appearing on the extreme left, a thin line of green radiance swept across the vastness of Orbitsville, moving so quickly from east to west mat it crossed her entire field of view in less man a second.

Jean gave a sharp scream, keyed up to believe that any change in the unvarying blackness ahead signalled the final impact, men as quietness and stillness returned — as life continued — it began to dawn on her that she had witnessed the unthinkable. The fleeting green meridian had been a genuine phenomenon, an objective reality.

There had been a change in the enigmatic material of the Orbitsville shell.

Facing imminent death though she was, Jean felt a near-blasphemous excitement. Spherology was the name given to the science which had been born two centuries earlier when teams had first begun to study the shell material, and it was a discipline which was characterised by total lack of success. Even when viewed through a quark microscope the material appeared continuous — an embodiment of the pre-Democritus concept of matter — and in two-hundred years of concentrated effort no researcher had been able to make the slightest scratch on it or to alter it in any way. After millions of man-hours of study, spherologists knew the material's thickness, its albedo, its index of friction, and very little more.