Synopsis
The book follows the experiences of three members of the royal household of the Sarl, a humanoid race living on the 8th level of the Shellworld of Sursamen, an ancient artificial planet consisting of fourteen nested concentric spheres internally lit by tiny thermonuclear "stars", whose layers are inhabited by various races. Constructed for an unknown purpose by a long-dead race called The Veil, Shellworlds are guarded and mentored by progressively more advanced species, up to the level of what the Sarl call "Optimae". Approximately 4000 Shellworlds are known, but almost 200 have been deliberately destroyed by another later, vanished race, The Iln; most, if not all, are also evidently equipped with mechanisms that activate randomly, either exterminating the inhabitants or collapsing the entire Shellworld. Like many Shellwords, the hollow core of Sursamen is known to be inhabited by a mysterious creature called a Xinthian Tensile Aeranothaurs, whom the Sarl worship as their World God.
The Culture is considered one of the Optimae, though Sursamen is not in their direct sphere of influence. Ferbin, the heir to the Sarl throne, has to flee his home level on the Shellworld after witnessing the murder of his father, King Hausk, by tyl Loesp, the King's second-in-command. Oramen, Ferbin's studious younger brother, is unaware of the treachery and trusts tyl Loesp fully. After Ferbin's disappearance, tyl Loesp takes on the role of regent, supposedly until Prince Oramen comes of age and can be crowned King.
The Oct, the mentoring species of the Sarl, meanwhile have been organizing the takeover of the 9th level of Sursamen, using the Sarl as their pawns. It becomes increasingly clear that they are searching for something hidden in the Nameless City, a metropolis buried under several hundred million years of sediment which is currently being stripped away by the giant Hyeng-zhar waterfalls. The 9th level was only recently re-colonized in a move by the Oct which was retrospectively validated, with reluctance, by the mentoring races.
Elsewhere, Djan Seriy Anaplian, another child of King Hausk, had left Sursamen fifteen years previously to become a member of the Culture, and of an organization called Special Circumstances (SC). Anaplian (the author uses this as her primary name, rather than Djan) decides to return to her home planet, originally simply to pay her respects to her dead father. On her way back, she joins up with the fleeing Ferbin and his faithful (but increasingly independently-minded) servant Choubris Holse, from whom she learns that her father's death was in fact a murder.
Other channels of intelligence indicate that the Oct are planning something mysterious on Sursamen. Special Circumstances asks her to investigate, and she meets Klatsli Quike en route, who turns out to be an avatoid (indistinguishable from human) of the Liveware Problem, probably an undercover SC ship. Her rather irritable combat drone (Turminder Xuss) stows away in her belongings, disguised initially as a dildo. Anaplian has had most SC enhancements disabled (the Morthanveld - in whose sphere of influence Sursamen resides - well know the fearsome reputation of such an SC combat team), but she begins to restore them, and Xuss will prove critically useful.
Returning to Sursamen, they realize that they have come too late – though Oramen, warned by several botched assassinations, had begun an open struggle with tyl Loesp, neither of them could (or wanted to) stop the excavations in the Nameless City before a fateful discovery – a member (or possibly a machine) of a long dead civilization known as the Iln is uncovered deep beneath the city and wakes. The Iln were responsible for the destruction of thousands of shellworlds before ultimately disappearing. The revived Iln's intention is the destruction of shellworld Sursamen. Its nature comes as a horrible surprise to humans and Oct both – with the Oct having thought that they were excavating one of the Involucra (the 'Veil') who had originally built the shellworlds and from whom they claim to be descended as a matter of faith. The Iln entity kills all present with a thermonuclear explosion including tyl Loesp and several hundreds of thousands of workers excavating the Nameless City (but not Oramen, who has been carried away – he dies of other wounds and radiation sickness shortly afterwards), before heading towards the core of the world, aiming to destroy Sursamen completely using antimatter.
Anaplian, Ferbin, and Holse head towards the core level, equipped with highly sophisticated SC-technology level combat suits. They are accompanied by Xuss and Hippinse, another of several avatoids of the Liveware Problem. The latter takes substantial damage from Nariscene weapons during its descent to the core, the constrained tunnel and the nature of the 4 dimensional shellworld limiting its defenses. The team is thus outgunned by the Iln, who has taken over the programming of a Morthanveld guard ship and twelve other drones secretly emplaced in the core. Xuss is MIA. Hippinse's parent ship, the Liveware Problem, disposes of all but two of the Morthanveld drones then sacrifices itself in a suicide attack on the Morthanveld guard ship. Hippinse himself is killed eliminating one of the remaining drones; Anaplian accounts for the last one, but the Iln remains too strong for the remaining compatriots, whose resources are seriously depleted.
In the end, the sacrifice of two (Ferbin and Anaplian) saves one and defeats the Iln. Ferbin is killed outright, but satisfies the Iln that the group are not harmful when disarmed and permits Anaplian a close approach. Despite her advanced armor, she is shredded beyond the point where a non-SC enhanced human would be dead, but she remains conscious enough to detonate the tiny grain of antimatter in her skull that provides power to her SC enhanced body.
In the epilogue, Holse, the lone survivor of the Iln encounter, rejoins his family after a long absence, accompanied by Quike. He declares his intention to become a political leader of the Sarl, with the secret backing of the Culture. From Holse's survival, the Culture could be presumed to have a reasonably complete picture of events; from the continued existence of the shellworld, one may infer that Anaplian's sacrifice successfully foiled the Iln.
The final body count is not immediately clear. Anaplian was backed up before leaving her Special Circumstances post, but, if restored, such a backup would not remember more recent events. However, part of her "insurance" taken out before the final confrontation may have been a more up-to-date backup. Similarly, the drone Turminder Xuss proper survived, but the destruction of his knife-missile mind-copy would mean memories of earlier events were most likely lost.
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