It depicts the effects of the opening of a connection between two versions of Earth in different parallel universes: the world familiar to the reader, and another where Neanderthals became the dominant intelligent hominid.
Geneticist Mary Vaughn, a professor at Toronto's York University, is called in to determine if the man really is a Neanderthal.
Mary is reeling from being recently raped by a masked man on the University campus, and finds this a welcome distraction along with the scientific opportunity of a lifetime.
Ponter and Mary forge a relationship as they strive for both their people's mutual benefit even as they struggle to work through profoundly different beliefs as a potential crisis looms for our Earth.
All barast women have synchronized menstrual cycles, and the meeting-times are set so that conception is unlikely — except every 10 years, when another generation is purposely conceived.
The separation is a voluntary and cultural thing, and people of both sexes are free to go where the other lives at all times, but find it physically and socially discomfiting to do so when two are not one.
While opposite-sex couples form long-term bonds similar to marriage, the same is true of life during the rest of the month.
Recordings are maintained after death; it is not made clear what the reasoning is for this and under what circumstances and or by whom a deceased person's archive can be accessed.
Any serious crime has a single punishment: the castration of the offender and all others who share at least half his genes (parents, siblings, and children).
This eugenic practice serves to keep any undesirable elements out of the gene pool without severely punishing an offender, beyond his loss of genetic heritage.
Past political assassinations did not even require weapons, given their physical strength, since a barast could simply murder their target using their bare hands.
Though the main purpose is to purge genes that could lead to criminality, it was once mentioned they had also sterilized people with low IQ in the past too, and raised theirs a standard deviation as a result.
Lower population levels and the absence of large-scale agriculture mean that many species exist which are extinct on the gliksin version of Earth.
It is heavily implied that the barasts did not spread to large areas of their world until after they had achieved a high level of civilization.
This is consistent with their hunter-gatherer lifestyle which favors high levels of knowledge concerning the land and low migration, including a general avoidance of danger.
It is theorized that this difference is an additional reason for the lower occurrence of extinction events: because of their higher intelligence, the barast were able to recognize far earlier in their civilization that over-hunting would deplete a species.
Barast swear words do not invoke religion or sex (given they lack the former and do not have taboos on the latter) but food decay, such as "gristle" or "green meat".
This leads to a lack of knowledge in certain areas, such as astrophysics, as such pursuits are stopped once they ceased to produce meaningful improvements in ordinary life.
Barast medicine has become largely automated, and most doctors, aside from first aid (excepting researchers), simply operate and maintain this technology.
The Barast do not find this disturbing in the least, which one Gliksin theorizes is because, as they are still a civilization completely composed of active hunters, they have been exposed to such scenes since childhood.
Additionally, given their strong sense of smell, barast surgeons do not wear face masks while performing surgery so they can use pick up any relevant olfactory factors to aid their work.
The story ends before any large-scale intermingling and rationalization of the two races' science can begin, so the ultimate outcome of detailed comparison between these viewpoints is unknown, though a magnetic pole reversal occurring on Earth causes a similar lack of religious/mystical belief to occur (following a surge) as human brains worldwide are affected (one result mentioned is peace in the Middle East as religious conflicts die out).