A starship has made the FTL leap to another star system -- a minor little sun, for the purposes of surveying the stars to make charts. Its crew was not so much selected as negiotiated. About a third of them are effectively in (temporary) exile. Others -- well, Billy Toyodo was sent because his uncle thought it would do him good to get off earth.
Except that they keep finding anomolies in their data about the star. They investigate and investigate -- and finally conclude that yes, it's aliens.
Someone thinks to tell the captain, and the argument they should flee with the news is shot down. Meanwhile, the aliens, in all their individual colonies, have noted the arrival and began to ponder it. When the ship reappears deep within the system, they realize these beings are not like them, the descendants of those who chose to live in space or the Colonists, and furthermore, have a form of FTL drive that they don't, one that makes FTL travel feasible.
They succeed in opening up communications, and things happen. Even though there is no real main character, only major ones, the book still is focused about the impact on both the Colonists (or Owlies) and the humans. One human becomes infatuated when he realizes they have no war. Another remains certain that the Colonists are their enemies. Many other talk with them just to talk. The Colonists suppress some knowledge about themselves, but it comes out when plots start to come to fruition.
The rest of the book involves intra-Colonist politics, drugs, hand-optimization of translation tables leading to truly oddly phrased conversations, gold, explosions, philosophical discussion of the truth, the conversion of ships meant to dive into Jovian atmosphere, sabotage, a trial, the reentactment of an ancient Japanese tale not quite faithfully and a daring rescue.
I particularly like that there are two characters in it who are clearly meant to be wise, and he succeeds in pulling it off. The only way I have ever seen any writer pull off wisdom: he ripped off historical wisdom and put it in his characters' mouths. Indeed, we are told where they get it. (No actually wise man is ashamed to believe what has been believed before.)