The novel concerns a xenological expedition to the planet World, where aliens live who have developed a strange form of telepathy or collective unconscious, "shared reality", which causes piercing "head-pain" whenever "Worlders" attempt to hold strongly differing opinions.
Simultaneously, an artificial satellite is found in orbit of the planet which has uncharted powers, and may be the key to winning a war against a xenocidal alien race, the "Fallers".
The space tunnels also lead to the discovery of the Fallers, an alien race who refused to establish communications and immediately launched a war, which they are winning.
Unlike humans, they did not discover the tunnel independently; it was, in fact, a Terran craft emerging into their home system that catapulted them onto the interstellar stage.
"Genemods" are applied in vitro, whereas those who adhere to the "Discipline" administer "neuropharms" daily to control their neurotransmitter balances, in a mix that can be altered depending on the activities of one's day and the mood one hopes to approach it with.
On his team are Dieter Gruber, a geologist; Ann Sikorski, a xenobiologist; and David Campbell Allen III, a graduate student in xenology.
When Orbital Object #7 is tested on setting one, it sends out a spherical wave that causes all nearby material higher than atomic number 75 (rhenium) to go radioactive—not by irradiating them with energy, but by manipulating the heretofore-untouchable strong nuclear force.
On World, Bazargan struggles particularly with David Allen, who is entranced by the forced altruism of shared reality and wishes to splice it into the human genome.
He also liaises with the head of a rich trading family, Hadjil Pek Voratur, who sees plenty of chances for profit in the Terrans' advanced technology.
Bazargan and Ann Sikorski eventually strike a bargain with Voratur, trading the secrets of antihistamines (for Worlders, flower-sickness is sacrilegious) for a chance to perform a "Lagerfeld" brain scan on him.
The Lagerfeld scan is unable to pinpoint a specific place in the Worlder brain where shared reality nests, and Ann concludes that it did not evolve and is not genetic; David Allen refuses to believe this, and begins to suspect a conspiracy between Bazargan and the high priests of World.
It appears to have crash-landed on the planet millions of years ago (precipitating a mass extinction) and is putting out prodigious amounts of radiation.
Just prior to this, Dr. Johnson receives a transmission from the diplomatic team containing Gruber's theories on the probability field, and realizes that this could explain the Fallers' new shield.
However, her speculation is short-lived; when Orbital Object #7 enters the tunnel and is subsequently destroyed by it, it fires off a destabilizing wave at its maximum setting (revealed in the sequel Probability Sun to have a range of about 6 billion kilometers, and to somehow be not susceptible to the inverse square law), which destroys the Zeus as well as all Faller craft, irradiates an outer planet in the World system, and then proceeds onward to World itself.
Kirkus Reviews wrote that the book is "twisty and compelling, brimful of ideas with Kress’s usual life-sized characters", and called it a "top-notch work from a major talent".
[1] Roland Green of Booklist wrote that "Kress' characterizations are as sound as ever, but many will be agreeably surprised at her proficiency with military hardware and action scenes.
"[2] Jackie Cassada of Library Journal wrote that despite "occasionally reading more like a drawn-out short story rather than a novel", the book is a "fine debut by a writer with potential to grow".