A Deepness in the Sky is the first Vinge novel that I read, and while it lacks the cosmological intensity of A Fire in the Deep, I think it holds up as the superior work.

In the distant future humanity has hit a plateau of development. Human planetary civilizations rise and fall over their century-long cycles, while the interstellar traders of the Qeng Ho skip from system to system in sublight ships, hoping to find a technological civilization worth trading with when they arrive. Just outside of human space is the OnOff star, a stellar anomaly that recently begun crude radio transmissions. The possibility of aliens inspires two great expeditions: a Qeng Ho trading fleet and one from the Emergents, a small interstellar empire that uses a unique form of neurological slavery. What they find is a civilization of giant spiders gone into hibernation, at the threshold of a leap into the information age. It's the most profitable time to arrive, and with the first contact the technological aliens, the value of the prize is infinite.

Above a frozen alien world the fleets collide, nearly annihilate each other in a flurry of nuclear sneak attacks, and the Qeng Ho and Emergents settle into an uneasy unified society. Both sides need each other for survival, and neither trusts the other. The only hope is to last until the locals Spiders develop a tech base that can be bootstrapped to space-flight. Qeng Ho 'peddling' is practically treason to the Emergents, who's use of Focused slaves (people infected with a specialized disease and turned into monomaniacal experts) is anathema to the basic concept of human rights. The Emergents have all the guns, but the Qeng Ho have a secret weapon. In hiding is Pham Nuwen, the legendary founder of the Qeng Ho and a practiced programmer-at-arms. All he has to do is evade the unblinking eye of the most effective police state imaginable, where the will of sadists is backed up by enslaved analysts capable of putting together the pieces of any plans. Meanwhile, the Spiders are facing their own annihilation, with the specter of a nuclear exchange overshadowing mastery of technology that would overturn their long history under the strange OnOff star.

This is a book of slow exploration of three alien societies--even the humans are foreign to us--and then rapid bursts of violent action. Vinge has a real eye for espionage, and the way that slow plans explode into violence and split-second decisions. He uses the multiple points-of-view to maximum effect, revealing how ordinary Qeng Ho see Pham Nuwen's disguise, and the plots of the Emergent dictators. Two technologies, the neurological Focus and the localizers (tiny internet-of-things chips) that Nuwen uses as his backdoor, stand out as some great sci-fi. The Spiders are deliberate cast as twee Victorian Heroic Engineers, a some-what grating narrative choice that is explained in book.

There are some similarities with A Fire in the Deep: Pham Nuwen, an alien society reaching new levels of technology, a Machiavellian antagonist, but this book handles the same themes with greater elegance and style, absent the hoary space-opera-isms of the earlier book.