A Fire Upon the Deep is an action-packed space opera that also manages to be a fascinating exploration of radically different modes of thought, in a rich and surprising alien setting. Vinge's cosmology is based on an addition to the laws of physics, the Zones of Thought radiating out from the galactic: In the Unthinking Depths towards the galactic core, intelligent life is impossible. In the Slow Zone, physics works more or less like it does in real life (and in setting, Earth is buried somewhere in the Slow Zone.) In the Beyond, FTL, intuitive computers, and other sci-fi supertech work. And in the Transcend, vast and cool god-like intelligences live mayfly lives, lost in their own contemplation before leaving reality entirely, and occasionally sending artifacts and emissaries downwards. The action starts when an human expedition into the Transcend opens a 5 billion year-old archive, and instead of building a God, unleashes an ancient demon called the Blight. Two ships flee, and one is destroyed while the other jumps to an uncharted planet at the bottom of the Beyond, crewed by a family and 150 odd children in cold sleep. They have the bad luck to land in the territory of a local dictator, Lord Steel, and the parents are murdered in an ignorant attack on their ship. The children are separated and captured, 8-year old Jefri taken by Lord Steel and 14-year old Johanna rescued by travelers and taken to the more liberal realm of the Woodcarver. Meanwhile, up in the transcend, Ravna, a human librarian apprenticed to a major interstellar communications firms, puts together a rescue mission with the help of Pham Nuwen, a legendary hu,am hero reconstructed from a spaceship wreck by a Transcend Power, and two Skroderider traders; aliens descended from a sea anemone-like creature, and given mobility and short-term memory through the use of carts. They escape an attack by the Blight by the barest of margins, and it's a chase for the highest stakes.

The break-out stars of the books are the Tines, the alien species that Lord Steel and Wordcarver belong too, which captures Jefri and Johanna. The Tines are a dog-like group intelligence. A single Tine is a pathetic creature, but four or six of them together form a mind as intelligent as any human, using ultrasonic 'mindspeech' to create a coherent identity. Vinge explores the implications of Tine biology with both ease and depth, avoiding lengthy info-dumps while clearly laying out an alternative course of development. Because Tines think in the ultrasonic, pack-minds must stay fairly close together, and two packs can't mingle without losing all conscious control. The gestalt intelligence that is a Tine can be stable for centuries, adding new members as older bodies fade away, but inbreeding limits the successful lifespan. Much of the political conflict on the Tine's world is between Woodcarver's slow scientific experimentation, and the radical and unethical efforts Lord Steel and Flenserists to remake minds entirely, using torture and novel architectures to create Tines with singular capabilities never before seen on their world.

Johanna and Jefri are thrown into this mess and exploited to advance Tine technology, starting with gunpowder. Ironically, Johanna fights against Woodcarver, and the more or less benign Peregrine and Scriber, while Jefri is complete taken in by Lord Steel. Since Lord Steel has the starship, and the communication link to Ranva, he gets actual how-to guides for kickstarting a stagnant tech base, including breech loading howitzers and radios.

Meanwhile, in the Beyond, Ravna gets to see how dangerous the universe is close up. The Beyond culture expects things like a Class 2 Perversion to show up from the Transcend every thousand years or so and turn a few planets worth of sentients into tele-operated zombies, but the Blight is a threat of different level, and human polities are utterly destroyed by a combination of the Blight an opportunistic genocidal aliens. Pham Nuwen is an uncertain ally, either a true hero or an elaborate fraud constructed from a few strands of damaged DNA and memories faked up from adventure stories. The Skroderiders are revealed to be unwitting agents of the Blight, their billion-year old species containing backdoors that enable them to be mind-controlled.

One aspect of the book which I'm ambivalent on is the Net of a Millions Lies. While FTL communication is possible, the low bandwidth means it looks and works a lot like USENET circa 1993. The idiotic flamewars and misconceptions percolating through the Net Messages Ravna reads are entirely familiar even on the contemporary web. I'm not sure if it's great world-building (somethings never change), or edges on too-cute. Regardless, the great investigation of the minds of the Tines, and hints at the vast powers of the Transcend, along with a high-octane adventure plot, make for an ambitious book that succeeds at all of it's goals.