It takes a very skilled writer to make unearthly aliens that are convincing, sufficiently alien to reflect my humanness through unfamiliar eyes. So I must say at the outset, that Timothy Zahn's aliens are all too human. However, he spins a great tale, bringing new ideas to seem almost familiar.
Imagine a railroad to everywhere...that is, everywhere in the Galaxy. You just need to get an AU or two beyond Jupiter's orbit, and the rest of your trip, except for a short rocket ride from the station to your destination, is similar to a ride on the Cannonball from Wichita to Omaha. This is the background setting of Night Train to Rigel, Zahn's latest galactic opera. He is really good at this.
There isn't a lot I can say without giving away too much of the plot. Zahn is just getting going with the galactic railroad idea. He also brings us a hive-mind entity with really big aspirations, a look into how high high finance can get when you've got a few colony worlds under your belt (who will be the first multi-trillionaire?), and some rather interesting blending of human and other.
I often take care to note if a book's plot has a labyrinth hidden underneath. (Short course: the difference between a labyrinth and maze is, you can get lost in a maze. A labyrinth has a single path, however it may wind around.) The oldest labyrinth tradition generates paths with three, seven, eleven, or fifteen circlings of the goal before one reaches it. You can get a three-turn path into a short story or novella, a 7-turn path into most novellas or novels, but few writers try for more than seven turns. I think this book achieves eleven turns, but I didn't count. Suffice it to say, there is double-, triple-cross, and greater here, enough for the most devoted of mystery readers.
I did say this is a mystery, didn't I? I guess not. But I find that the best science fiction is also good mystery writing. Sci-fi is about problem solving, as is mystery writing. When they are combined, the result is very satisfying.