Way back when I first starting reading science fiction, I mean, really reading science fiction, I was in my early 20's and didn't have the honor of having anything like mentor to bring me into the genre. I had no internet, no real filter to help me weed out the great from the not so great. 
 I ended up picking a few books early on that just happen to be giants in the field. One of them, A Fire Upon the Deep, hadn't been in paperback very long before I picked up a copy. I can't help but wonder what would have happened had I passed it over for something else at the time. Little did I know that I was getting one of the best science fiction books ever produced. And something that made sure that I would always, always, love science fiction for the rest of my life. 
 I just finished reading this for the fourth time. I read it initially back in the early 90's, then again only weeks later. Afterwards, I put it away until A Deepness in the Sky was released 7 years or so later. Then I picked it up and read it again. Well, now that Vinge has finally put out a true sequel (nearly 20 years later), I read it again. 
 It took me all of three pages to get right back into the story again. I'll do my best to give a synopsis that doesn't serve as a spoiler. 
 The galaxy is a stratified place, the laws of physics aren't uniform across it. If you are unlucky enough to be a civilization whose world falls within the 'slow zone' you are limited not only in how fast you can travel (relativity ruled - you know, like on earth) but also by how powerful a computer you can build. Within the slow zone, there are limits on how far a society can progress. 
 Stay with me here, this is important, the next strata is a region on the outer edges of the galaxy where FTL is possible, more elegant materials and computing are available. Truly sentient AI still isn't possible here, but this is where the civilized citizens of the galaxy reside. Humans have migrated here after eons of living in the slow zone. This place is called "The Beyond." 
 Okay, almost done. At the very fringes of the galaxy lies "The Transcend." This is where an anything goes sort of approach to physics and computation reside. Folks that live here are essentially post-singularity societies. The entities here are godlike and are either indifferent towards those in the lower zones, or if they do interact, they are often mischievous, toying with the lesser races, the goal of many beings in the beyond is to migrate to the transcend, becoming like gods and leaving behind who they once were. Beings that live here are simply referred to as 'Powers." 
 Got all that? That isn't giving away too much, as there is map at the beginning of the book that sorta outlines these layers where the laws of physics change. It's really important to understand the story. Of course, the beauty of the tale is that the nuances of these layers, and what it means to the people who live within them, but I won't go there. 
 Some people, or races, are full of hubris - humanity chief among them. A small scientific community has set up a base at the very edge of the Beyond, and has made some explorations into The Transcend, and while there, they stumble upon a library of sorts, something untold billions of years old and forgotten by the entities that live in this region of the galaxy. 
 The promise of migrating to The Transcend, of humans becoming gods themselves, leads them to unleash something that was locked away from the universe. An ancient terror that even the god-like entities of The Transcend know nothing of. 
 Realizing what they've done, the humans flee from what they've unleashed, but with what they hope is the key to stopping the monster that threatens to destroy the galaxy. The survivors end up on a primitive world in the low beyond (close to the slow zone) where nightmares like this god-like monster cannot exist (because of the physics issues I mentioned earlier). Too bad that all that has survived is a couple of little kids. 
 This primitive world has its own society, beings with their own goals, dreams, and visions of one day flying among the stars. The fate of all life in the galaxy rests in the hands of a medieval warlord on a backward planet who sees only what these children might do to help him defeat his enemies. As an aside, this alien planet has some of the coolest aliens ever devised. 
 This is perhaps the most satisfying novel I have ever read. It's hard to be objective about it now, as it has played such a role in the books I read after. But after reading it again over the past two weeks, I am glad that the novel has aged so well, nothing about it feels like it was 20 years old. If I read it for the first time today, I would be amazed at how well done it was. It has big ideas, an epic scope, an emotional story, and a satisfying conclusion. It's like Arthur C Clark, Olaf Stapledon, Stephen King, and JK Rowling all collaborated on a super novel. 
 Best. Book. Ever. 
 Er, I might need to qualify that. It's so great because it not only has an identifiable story arc with the children, it also has that high minded, epic sense of wonder that I'm always looking for. I understand that it might not be for everyone. But this review isn't for everyone, it's for me.