This is one of Ian M. Bank books in his Culture series, an entry about halfway through and written in 1996. Its a series fans of space science fiction like Star Trek would love, but its has its own peculiarities that might make it hard as an introduction to the genre. It's setting is one of a large galactic civilization whose citizens live almost entirely on ships and very large space stations where most of the management and direction is handled by very, very advanced artificial intelligences called Minds.

And this book in particular, Excession, is written quite a bit deeper on that aspect as the plot revolves almost entirely around how these Minds react to a very strange object discovered in a quiet part of the galaxy.

I really enjoyed the thrilling and mystery aspects of the story, leaving some things unknown all the way to the end. Especially the reveal of just what exactly the titular excession is. In the book its introduced as a "Outside Context Problem", a situation in which a much less advanced civilization encounters something entirely more advanced and nearly incomprehensible. This object is scanned and found to be capable of seeming traveling across universes. An analogy would be life living in 2 dimensions along the surface of a sphere finding something that can travel between entirely different spheres.

However, some aspects of the story, various plot lines with one in particular, resolve in a somewhat unsatisfying way. Though it is used to reveal just how these Minds think, react, and plan. As a whole trying to follow some of the stories can be difficult, especially the large number of individual ships that communicate in the story. I suspect rereading the book a couple times might help make connections and understanding.

All in all however I quite enjoyed it and further reinforced my desire to continue the series. I have started on Look to Windward, which a synopsis indicates it deals with the distant aftermath of the events in Consider Phlebas.