Pebble in the Sky was Isaac Asimov's first SF novel, which is really a pretty amazing thing to contemplate when you think about it: kind of like knowing what the first brick in the Great Wall of China is.
The story is a sheer treat. Though the science may be hopelessly out of date, Pebble nonetheless shows off Asimov's then-developing talents for clarity and accessibility to dazzling effect. Joseph Schwartz is a retiree in post-WW2 America who is out for his morning stroll when he is suddenly transported in mid-step tens of thousands of years into the future, where the Galactic Empire ruled by Trantor is in full-flower, the origins of humanity have become lost and enshrouded in myths and theories bandied about by the myriad human races who have settled across the cosmos, and Earth is nothing more than a "pebble in the sky," a grungy little ghetto world no respectable person would spit upon.
Finding himself amongst people whose language and culture he cannot hope to understand, Schwartz is taken to the city of Chica (a pretty obvious bastardization of the name Chicago) where he is made a test subject for a machine called the Synapsifier, which is rumored to increase human learning capacity by increasing synaptic discharges, but which has also had an annoying habit of killing most of the animals it has been tested on to date.
It just so happens that, right at this time, an archaeologist from a distant world named Bel Arvardan, a controversial figure for his support of the theory that the Earth is the origin of all human life, has arrived on Earth in order to gather evidence to support his theories. Part of this evidence is the Earth's radioactivity. Life should not be able to evolve on a planet so radioactive. Could there have been a nuclear war at some point that irradiated the planet, thereby establishing that there was human civilization thousands of years before the earth became radioactive at all? (The whole plot element involving Earth's radioactivity is one that Asimov acknowledges is no longer scientifically valid, in an afterword to the Del Rey edition above.)
As the plot begins to get deliciously twisted, we learn that the Council of Ancients — the ruling body on Earth who wield a power similar to that of the Roman Catholic Church in medieval times, particularly in regard to a law requiring all citizens to be euthanized at age 60 so that Earth's minimal resources are not taxed by overpopulation — suspects that Arvardan is actually plotting with the Empire to gain control of the Synapsifier for themselves, so that the Empire can enhance its own people with it and crush the Earth once and for all. They also suspect that Schwartz, who has popped up out of nowhere and has no records of any sort, is the first Imperial subject intended by the Empire for Synapsifier treatment. We know that this is all paranoid hogwash (Schwartz was simply taken to the Synapsifier because he couldn't understand any of the language or customs of his new, alien surroundings, and the farm family that took him in assumed he was merely an idiot), but it's a story element that makes the plot wonderfully layered. Starting as a story about time travel, Pebble in the Sky moves through politics, subterfuge, romance and espionage, finally ending up as a grand space opera of interstellar rebellion.
It's easy to see why novels like this one and The Caves of Steel put Asimov on the map. These early novels are spun with the effortlessness and near-perfection of a natural talent working at full bloom. Pebble in the Sky cannot help but show its age at many points. One particular thing that nagged me was that for a real SF novel, one in which the science was presumably important, Asimov never really adequately explained how Schwartz got displaced in time in the first place. But I had such a fun time simply reading the story, I was more than happy to ignore its occasional cracks. After all, this book was only the first brick — or pebble — in the Great Wall.
After several years out of print, Pebble in the Sky was reissued by Tor in hardcover in 2008.