If I hadn't been reading this as a nominee for the Endeavour Award, I probably wouldn't have finished it. Frank Compton is the protagonist. He used to work for the UN, but he has a problem with politically ill-advised honesty and got fired. As the book opens he's being given a train ticket by a guy who's close to dead from some kind of sci-fi projectile weapon. Compton doesn't know anything about why the guy's there or why he's being given this ticket, so of course he goes and gets on the train. But it's not a choo choo, it's an FTL conveyance with a stop out by Saturn that ties the inhabited systems of the galaxy together. Once he gets out there he finds out it's the "spiders" who run the railway who've given him the ticket cause they have a job for him. They have had a prescient vision of a big war and want him to stop it before it starts.
I have a lot of gripes with the book, but they all boil down to the fact that the author's hand is far too evident for my taste. Compton gets shuffled around by different players in the story for reasons that while they aren't completely arbitrary are pretty close to "Zahn says so". The capabilities of technology are arbitrarily limited or expanded to move the plot along too. I could go on, but I'd rather just put this one behind me. Okay, one more: it's twice as long as it needs to be. Read something else.