Neural mods can be used to carry software in the brain, instead of on computer, from simple calculators to complex analysis. They can be used to control the body's responses and hormone levels, to induce sleep, wake at certain times, even to slow or raise metabolism.
They can also be used to gain a particular belief. When the mod is used, then the belief is complete and absolute.
In this future, the earth has been quarantined. A giant bubble that encompasses the solar system, cutting us off from the rest of the universe, and taking away the stars forever.
The main character, Nick, is like a futuristic gumshoe detective. He is hired to investigate the disappearance of Laura, a retarded woman, from a locked institution. There are no apparent motives for kidnapping, and she cannot even open a door by herself. Yet she had apparently been found outside before.
When he finds her location, he is captured by the people who have her and given a loyalty mod. He now believes that the Ensemble is the most important thing in the world. He is employed by the Ensemble as a security guard. After six months, he is told that he is being transferred, but that not everyone in his new job knows about the Ensemble, and he must never speak of it.
Nick's new job is being the bodyguard of a woman in an experiment. Po-kwai sits in a room all day, watching photons go up or down on a screen and reciting their direction. As time goes on, Nick learns that the experiments are related to quantum physics. The act of observing the experiment collapses the wave function so that the photon goes either up or down.
Po-kwai is testing a new neural mod, which should enable the observer to collapse the wave in whatever way they want to. This works by first inhibiting the part of the brain responsible for the collapse, then choosing an outcome. The time before the wave collapses contains all potentials, and Po-kwai calls it being "smeared".
Nick knows that the Ensemble did not create the mod, they patterned it on Laura's brainwaves. That Laura is able to control the collapse naturally, and that is how she got out of the institution.
Nick is approached by Dr Lui, one of the researchers, who explains that he too has the loyalty mod. He tells Nick that because the Ensemble is a mysterious group within their organisation, they cannot trust them to have the Ensemble's best interests at heart. The only ones who can be trusted are themselves, because they cannot be disloyal. Nick experiences a revelation that anything he chooses to do must be good for the Ensemble, because he cannot choose otherwise, and is effectively free.
He soon realises that he can manipulate the wave while Po-kwai is asleep, using her neural mod, and begins to experiment. He plots with Lui to steal the mod from the headquarters while smeared, choosing the optimal outcome to ensure success.
Meanwhile Po-kqai is discussing disturbing ideas with him, that perhaps the reason they were quarantined is because they were collapsing the waves further out in space. She suggests that perhaps there are species who live their entire lives smeared, and we are effectively destroying all their other possible selves by observing their part of the universe.
On the night of the break-in, while Nick is stealing the mod, he encounters Laura. Her smeared self is fully capable and speaks to him about the consequences of releasing the mod. She is the avatar of a bubble-maker, and Po-kwai was correct about the reasons for our quarantine.
Laura claims that their smeared selves make an entity that is not the same as their normal self, and that Nick should be wary of this.
Nick is halfway back when he is pulled over by Lui. Lui claims that there was a bomb alert at work, and they have realised Nick has left his post. Lui takes the neural mod.
Nick quickly realises that Lui intends to modify the vector and distribute the mod to everyone, making smearing standard. Although Nick tries to stop him while smeared, trying to pick the optimal outcome, he fails. He understands that his smeared self chose not to be destroyed by the collapse of the wave.
As morning breaks, reality unfolds, as every possibility becomes true.