The novel concerns a military 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.

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.

No Faller has been captured alive—they prefer to suicide or kamikaze—but forensic examination of corpses indicate they evolved separately from humans, instead of being seeded by the progenitors.

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.