Long ago, the legendary Vo'lach retreated to their homeworld and sent out robot agents to sell deadly, planet-cracking weapons to the other species of the galaxy -- on condition that the purchasers use the weapons to build an empire strong enough to defeat the Vo'lach when they come to destroy them. But now Vo'lach weapons have begun to malfunction in surreal and pacifistic ways, and the armies of the galaxy want someone to complain to. When Morry, the 12-year-old head of the galaxy's most notorious criminal family, learns of the problem, he realizes that if he can find out what's affecting the Vo'lach weaponry and control it, he will possess the mightiest army in human space. To this end, he activates a Ninjucoid assassin and downloads a copy of his own mind into it to ensure that it doesn't fall victim to the strange sensory distortions which have turned his other assassins into manicurists and flower arrangers. Eventually the Ninjucoid-Morry finds the trail of a Vo'lach Negotiator, and pursues it to the distant world of Canopus IV.
Benny is asked to accompany a field expedition to Canopus IV by Clarence, a representative of the People who takes the form of an angel. Apparently a minor problem on Canopus IV has the potential to affect the People, and due to the Treaty only Benny can deal with it. Canopus IV is the only source of the rare mineral futurite, which can retard and reverse the passage of Time, and is also the location of the Spire, a 300-kilometre-high structure which Professor Malkovitch Fellows believes is the source of the mysterious "dark matter" which holds the galaxies together. It is also populated by a race of reptilian humanoids, who scratch a meagre living out of a soil poisoned by fragments of futurite. The prospectors from the bank which recently lost the lien on Canopus IV's mineral rights never attempted to contact them, but shortly after their arrival Benny and her fellow archaeologists are captured by Canopan natives who speak near-perfect English. Apparently the Spire, regarded by the Canopans as a creation of the gods, grants the priests of Canopus IV the ability to see into the future. Benny tests this ability for herself and sees a vision of herself expelling the expedition's medical officer, Jane Steadman, out of an airlock.
The Priest-King Tenomi III agrees to let the expedition study the Spire on condition that they lead another expedition to find the Canopans' gods, the ancient aliens who built the Spire. When Tenomi and Fellows compare notes, they conclude that these gods must be the Vo'lach. Benny accompanies the expedition to find Vo'lach Prime, but what nobody knows is that they have been infiltrated twice. The crippled priest Mandir, for reasons of his own, has been capturing and torturing human prospectors for years and has managed to contact a Vo'lach Negotiator. While buying weapons of mass destruction, he informs the Negotiator -- an unintelligent machine capable of mimicking sentience -- of the expedition's purpose, and it disguises itself as one of the party and accompanies them to stop them from setting foot on Vo'lach Prime. Another member of the expedition is killed and replaced by the Ninjucoid controlled by Morry.
The expedition's navigator compares maps inscribed on the Spire to maps of the current astronomical era. The pulsars on the maps have slowed down over the intervening millions of years, and for some reason the Vo'lach maps have no quasars on them; nevertheless, the navigator is able to locate what seems to be Vo'lach Prime in the Sadr system. Someone apparently tries to poison Tenomi, but due to the nature of Canopan biology this has little effect on him. Steadman suggests turning back until they find out who is responsible, but then apparently falls victim to another trap when someone programmes the computer to seal off the medical bay and pump it full of inert gas in what seems to be another attempt on Tenomi's life. In fact, Jane is the one who has been replaced by the Vo'lach Negotiator, and it pretends to fall into a coma, having calculated the probability that its nature will be discovered if it does otherwise.
The expedition arrives in the Sadr system and finds Vo'lach Prime, which is inexplicably the second planet in the system -- and which is devoid of life and is undergoing continuous nuclear bombardment from unintelligent machines left to watch over it. The crew manage to convince the guardian machines that they are here on business and must land on the planet to continue their talks, but the Negotiator disguised as Steadman gets to the landing bay and sabotages the shuttle, which thus deviates from its planned flight path and is shot down. The survivors land in the ocean, where the distress call from the damaged Negotiator attracts a patrolling submarine. Unable to determine which of them is the Negotiator and which are illegal life forms which must be exterminated, the submarine rescues them all, and once inside they find themselves protected by the software which runs the ventilation system. Over the millions of years since the Vo'lach wiped themselves out, the Air Vent has developed a mind of its own, although it has been careful to hide this fact since the Great Plan requires the eradication of all sentient life on Vo'lach Prime.
The only casualty of the shuttle crash appears to be its young pilot, David Foreman, although nobody is able to explain the unconscious Jane's presence. Benny, Captain Johansen, Tenomi and the priest Geth manage to convince the submarine's checking mechanisms that they are Negotiators, but Steadman is too damaged for repairs, and the submarine requests a decision to expel her or recycle her for parts. Realizing that revealing Steadman as a life form would mean all of their deaths, Benny has no choice but to fulfill her own prophecy and expel her from the airlock -- and the Air Vent then belatedly informs her that Steadman was really the Negotiator all along. The Air Vent also informs them that after the Vo'lach built the Spire, they experienced a vision of the future so horrible that they committed mass racial suicide. They left behind them only the ghost devices, non-sentient machines which continue to carry out their programmed imperative to supply weapons to the rest of the galaxy and prevent sentient life from ever evolving on Vo'lach Prime again. Benny realizes that "Steadman" must have been responsible for poisoning Tenomi, in an attempt to force the expedition to turn back without actually killing anyone.
Back on Canopus IV, Mandir and his followers stage a coup and take the human archaeologists prisoner. The Canopans believe that the Spire is the only source of knowledge, but the visions granted by the Spire are patchy at best and are frequently misunderstood, and Mandir has grown to hate the gods with a passion. He forces his captives to translate the "ghost languages" of the future for visions of weapons, with which he intends to wage war against the gods. Fellows discovers that the visions are a side-effect of the Spire's true function, which is to draw matter back in time from the future and use the resulting tachyonic flow to generate anti-gravitons -- the dark matter which holds the galaxies in place and prevents the Universe from expanding into oblivion. The eccentric Elspet Vespatrick concludes from the fact that no Vo'lach can be found in the "ghost languages" that the Vo'lach are truly extinct. Mandir isn't interested in these trifles, however; he only wants weapons. Fellows, who has always believed in technology as a force for good and progress, slips into a state of shock as his translations of the Spire's visions reveal an endless future of war, death and suffering, brought on by Mandir and his followers.
Tension develops between Tenomi and Geth, who admits that Mandir asked him to go on the expedition in order to find a way to kill Tenomi and blame it on the gods. He accepted in order to prevent Mandir from finding someone else who would do as he asked, but has since come to believe that something is seriously wrong with Tenomi. When Geth attempts to kill Tenomi, Tenomi is revealed to be Morry's Ninjucoid in disguise. The Air Vent manages to beach the submarine, where a Factory which has also successfully hidden its sentience is waiting for them. Morry's attempt to kill the others, shooting Geth in the arm in the process, finally alerts the submarine's automatic checking systems that its passengers are organic, but with the Air Vent's help, they manage to escape to the Factory. There, they find David Foreman waiting for them, implausibly claiming to have swum ashore.
The Factory reveals that the malfunctioning weapons have been suberted by Vo'lach Wonder Lubricant, a nanoscopic oil which has itself evolved into a sentient life form. The Factory uses a stockpile of fusion bombs to blast itself into orbit, seeding the fallout with iridium to make the explosion appear the result of a meteorite strike. Morry gets to a weapons control centre, where he remote-launches a pair of planet-busting missiles from the first planet of the system -- which is revealed to be an artificial weapons platform, thus explaining why Vo'lach "Prime" is the second planet. Morry is then caught and torn apart by Vo'lach exercise equipment, infected with intelligence by the Wonder Lubricant and spurred on by the Air Vent. His mind returns to his body, only to find too late that his factotum has taken up an offer from another crime syndicate and killed him in his absence.
The Factory apparently ditches the planet-killers and returns to Canopus IV, where it intends to set up shop selling refridgerators to the galaxy. But its proximity to the Spire activates its fail-safe programming, and it lands on top of the Spire, where Mandir is waiting for it. Fellows and Vespatrick have finally realized the truth; the Vo'lach foresaw that their descendents would bring endless war to the galaxy, and destroyed themselves to prevent it from happening. But they misinterpreted the vision; their "descendants" are the Canopans, whose society was shaped by the influence of the Vo'lach, and Mandir, consumed by his hatred of the indifferent gods and the people of the galaxy who stood by and did nothing while his people suffered, is about to launch the war which drove his gods to suicide.
Benny and his friends are caught by Mandir's troops, but the planet-killers arrive at Canopus IV and Benny realizes that they're homing in on a tracer Morry shot into Geth's arm. She instinctively shoves Geth's arm into the tachyon flame in the centre of the Spire; the pain is agonising, and the outcome is horrific, as the homing mechanism survives the dissolution and is catapulted back into the past -- followed closely by the planet-killers. They explode at the moment of the Spire's creation, and the Vo'lach conclude from their analysis of the subatomic fragments remaining that weapons from the future of their own world were used to destroy the Spire; although they do not understand why, they conclude that it must not be created. Therefore the events which led to the planet-killers entering the Spire never take place, which means they don't explode and don't destroy the Spire, which means that it is built, which means the planet-killers destroy it...
Minor subatomic variations in each turn of the cycle result in major shifts to history. The time-travellers of the galaxy stand by outside linear time and watch until an equilibrium is reached -- a history in which the missiles explode, far enough in the past to damage the Spire, but not far enough to prevent its existence. In this history, the Canopans have been torn apart by religious warfare ever since the Spire was damaged, and Benny blames herself for this -- and for the worse to come. Since the Spire functioned by drawing matter back from the future, that future was fixed in place once matter from it began to exist in the present. By destroying the Spire Benny has returned quantum uncertainty to the Universe, and she may have just ended the lives of her friends from a future which may now never exist.
Benny nearly commits suicide when she realizes the extent of her crime, but thanks to a slight modification to history made by David Foreman -- a time-traveller who had been observing events undercover -- Clarence arrives just in time to save her life. He assures her that the Spire was a paradox in itself. Quasars are the result of the material flung into the past by the Spire, which is why they did not appear on the Vo'lach maps; they didn't exist in the past until the Spire began to put them there. If the Spire had continued to operate and send matter back in Time, eventually enough "dark matter" would have been generated that the Vo'lach would have seen no need to build the Spire; thus another, much larger historical loop would have occurred, and by creating and breaking a smaller loop Benny has prevented a major temporal catastrophe. She is reassured, and Clarence decides not to tell her that God chose her to do so in a way that would ensure the best possible outcome for the People.
Source: Cameron Dixon