Bren Cameron has the job of the paidhi, the sole point of contact between the human Lost Colony on the island of Mospheira and the alien atevi on whose planet the humans are living. While Bren enjoys being a diplomat/translator/linguist/xenologist, it's not what you'd call an exciting job. Some excitement is added when the aiji, the head of the atevi government, gives him a handgun as a gift, even though it's highly illegal for a human to posses a gun. It then gets much more exciting when, two weeks later, an assassin breaks into his apartment and he's forced to use the handgun in self defense. The attack leaves Bren baffled, since although there are plenty of conservative atevi who hate humans enough to want him dead, the conservative atevi have always hated humans, but no one has tried to have the paidhi killed in the nearly two hundred years that the office has existed. And thus begins C. J. Cherryh's book series on inter-species politics and intrigue.
Detailed background story
The Faster Than Light starship Phoenix is sent off to construct a self-sustaining Space Station, carrying as passengers the civilians who will build and then operator the station. However, while travelling through Hyperspace a should-be-impossible accident happens, sending the ship a much further distance than should have been possible, so far that no known star is visible through the telescopes. With the little fuel they have left they travel to the nearest star system which might have a life bearing planet. While the system does have a life bearing planet, it's already inhabited by the sentient atevi, so the humans stay in space, living in a Space Station they build in orbit around the atevi's planet.Two hundred years later, there are two factions of the descendants of the original humans, and tensions between the factions have reached the breaking point. One faction builds jerry-rigged landing vessels and use them to land on the planet on the island of Mospheira, while the other faction takes the refueled Phoenix off into space, intent on finding long lost Earth. The humans who landed make contact with the atevi (who were just entering their Steam Age) and the humans and atevi seem to be getting on well. However, each species makes the mistaken assumption that the other species has the exact same sort of government and power structures as they do, leading to lots of misunderstandings. Twenty years worth of misunderstandings lead to the War of the Landing, which almost wipes out the Lost Colony. Fortunately, the leader of the largest atevi government struck a deal with the colony, which came to be known as the Treaty. According to the treaty:
All atevi would evacuate from the island of Mospheira, leaving it entirely to the humans.
The sole point of contact between humans and atevi would be the newly created human office of the paidhi, who would receive extensive training in the cultural and psychological differences between the species so as to avoid any further misunderstandings.
The paidhi would be the only human allowed off the island.
The humans would slowly hand over their technological knowledge to the atevi, faster than the atevi themselves could develop it, but not so quickly that it would cause any societal disruption.
These novels contain examples of:
Bizarre Alien Psychology: The main character has to train himself to think like aliens in order to be an ambassador to them.
Blue and Orange Morality: If an atevi contracts with the Assassin's Guild to kill someone, the target is informed of the fact ahead of time. If, in spite of the warning, the target is killed, it isn't considered to be murder.
The atevi view some aspects of human society this way. As an example, when Bren's fiancée unexpectedly breaks up their longer long distance relationship and marries another man, Bren's atevi bodyguard considers it to be an unthinkable betrayal.
Fantastic Racism: Even the very progressive Western Atevi generally distrust Humans. The Eastern Atevi outright hate Humanity and if given the chance would start a second war.
Genki Girl: Played with Cajeiri who is in love with Human Culture, and hangs around human friends and has no idea about proper Atevi etiquette, because, he was in Space for 2 years without any other Atevi his age.
Good with Numbers: The other thing which distinguishes the atevi mind from that of humans (taking second place to their inability to understand love) is their facility with math. They can instantly and accurately count things, have a photographic memory for anything they count, the adult version of their language requires doing simple algebra to formulate grammatically correct sentences, and atevi cultures treat numerology with the same fervor that human cultures treat religion. Bren's chief bodyguard would be considered a mathematical prodigy by human standards, but chose a career having nothing at all to do with math.
Humanity Is Infectious: Averted. No matter how much exposure atevi have to humans, they'll never acquire (or even understand) human emotions involving affection, because their brains are wired differently than human brains.
Hyperspace Is a Scary Place: Well, actually it's a dull place, since hyperspace has the side effect of making everyone muzzy headed. When combined with the cabin fever of year long trips, this can lead to quite a lot of stress.
Atevi infectious diseases don't affect humans, and visa-versa.
Many atevi teas and seasonings contain alkaloids which are poisonous to humans.
The same alkaloids which are poisonous to humans are essential nutrients to atevi, so an atevi attempting to subsist entirely on human foods would suffer from vitamin deficiency, and eventually die.
Atevi foods contain carbohydrates, fats and proteins which are digestible and usable to humans, and visa-versa for the atevi.
There's nothing in human foods which is poisonous to atevi.
Reasonable Authority Figure: Tabini is pretty much this. Considering how merciful he is and how he's actually never lost his patience with the Ship-humans and their constant infighting. Human President Shawn Tyers is this as well.
Rubber-Forehead Aliens: The only visible difference between humans and atevi are that the atevi are taller, have gold colored eyes, pitch black skin (darker than even the darkest human skin, and shading to grey as it gets lighter), pointed ears, and no facial or body hair. Oh, and their sweat smells like petroleum products.
Their hair is also a different texture than humans', to the point where they find it odd that human hair won't stay perfectly braided during physical activity, and their eyes are reflective in the dark.
The Kyo are also another example. They look like a larger and thicker version of humans, but they think very differently.
Humans have delayed handing over computer technology to the atevi, since computer hardware and software is full of manipulating numbers. If a customer database assigned customer numbers to people, some atevi would take offense at being assigned an unlucky number. If the database was changed to only use customer numbers internally, those atevi would take offense at secretly being assigned unlucky numbers.
When the atevi first started using aircraft, each atevi would determine their flight path according to whatever brand of numerology they used, completely ignoring air traffic control. It took a serious aircraft disaster before the government could effectively force all pilots to obey air traffic control.
Atevi numerology is much more complex and wide-ranging than the human equivalent, since one of the more popular schools of atevi numerology includes "Faster-Than-Light Travel is impossible". Humans had to avoid revealing that they arrived in the atevi's star system via Hyperspace since that would have pissed off so many atevi it might have lead to another war, that's how seriously atevi take their numerology.
Space Is Cold: The only notable science mistake Cherryh makes in the novels is that unheated portions of Space Stations and starships are extremely cold.
Spot of Tea: Any meeting with atevi, whether for business or socialization, is probably going to involve drinking some form of herbal tea. Unfortunately for Bren, many atevi herbs are poisonous to humans, so he has to be careful about what he drinks.
What Is This Thing You Call Love?: Atevi are completely incapable of feeling any emotion involving affection, since their brains are wired differently than humans. Having no common point of reference, they can't even understand it. The closest translation they have for "like" in the sense of affection is "like" in the sense of "I really like salads".
This is probably the largest cause of on-the-job stress for Bren: he spends 99% of his time surrounded by people who he likes who not only will never like him back, but who will never even understand what it means to like someone.
The reverse also applies, since the atevi feel an emotion unknown to humans, manchi. Humans can sort of understand it, since it's sort of like loyalty and sort of like a flocking instinct, but humans can never fully understand it, never grasp it at a gut/intuitive level, and never ever actually feel it.
The Xenophile: Bren has a rather large fascination and affection for the Atevi and their culture. So much so that he eventually drops any pretense of taking orders from Mospheira and openly becomes Tabini's agent instead, and begins living permanently on the Mainland. Certain humans are... not happy about this.
Cajeiri the 8 year old kid of Tabini is obsessed with Human Culture, and can speak fluently several languages. This is not however a good thing as Cajeiri has difficulty relating to his own kind.