Defender [Foreigner 5] by C. J. Cherryh
This book is part of a "Foreigner" group of books by the author. It's a sequel to Precursor.
The Foreigner series of books involves a human starship, Phoenix, which has lost its way - not knowing where in the galaxy it's ended up. They reach an Earth-like planet. A portion of the people end up descending to the ground, the starship goes to explore other stars. The planet already has a native race that's more-or-less humanoid in physical terms, if not thought. Communication is difficult. The natives and the humans work under different assumptions and conflict results. The humans end up relegated to a single island. The humans interact with the natives through a single diplomat. Initially, the natives had limited technology, but are gaining it from humans via trade for resources. After 200 years, Phoenix returns concerned about hostile aliens from another star system. The books feature an extensive look at an alien society and issues of successful communication with aliens. Much of the story deals with political intrigue and maneuvering.
On Phoenix, rumor spreads that Captain Ramirez made statements as he was dying - that Reunion (the space station attacked by aliens in another star system) wasn't destroyed. Members of the Phoenix crew have family on Reunion. They want to know what happened to them and help their kin if they're still alive. This leads to planning a mission to return to the other star system.
This is the middle book of the second trilogy. It's not so likely to work as a stand-alone novel.
As with other books in the series, much of the story involves various intrigues between different native groups, the human government, other human groups, and the starship with its politics. Much of the turmoil takes place in the minds of Bren and others as they try to find ways through the labyrinth of plots and alliances.