Even as a grade schooler I found that story completely fascinating. Each chapter describes huge sociological changes in mankind's history starting from some time in the near future where people begin abandoning the cities. The explanation, among other things, is that the population is being fed via hydroponics so farming the land was no longer necessary. Land becomes so cheap that people abandon their homes and move to the countryside (has some parallels to what's going on in housing today!). For continuity, the book follows several generations of the Webster family. Jenkins is their robot butler who is passed down through the ages. We see a group of smart "mutants" that take to the hills and start a society. They discover that the collective intelligence of ants has no limits save for their need to hibernate each year, and by removing that constraint for them, the ants eventually learn to build tiny robots that enter the brains of animals and turn them into slaves, building structures for them and rockets to travel into space. The mutants ultimately figure out how to create doorways to parallel universes into which they depart. That's just one of many side stories. Men learn to change their bodies so they can live on Jupiter, and when they discover that in the new body form, the planet is a paradise, they eventually abandon earth altogether for a life of bliss. I believe some stay behind in some sort of induced coma living a virtual reality life of their choice. Meanwhile, after having experimented with imparting vocalization skills to dogs, man's best friend soon learns to communicate with him, and then eventually takes over the planet after human kind has fled to Jupiter. Jenkins and the other robots stay behind to serve the dogs.
One other aspect of the book that I still find particularly amusing is that it pretends to be a series of legends, published by the dogs in the distant future, about their alleged mute past, and about this creature called "man" who they supposedly once served. Each chapter is preceded by a discussion of the prevailing views of contemporary scholars (dog scholars) about the authenticity of various parts of each tale. The satirical irony just oozes out of the pages.
Now I'm sure that all sounds quite ridiculous, but it was perfect for sparking a young boy's imagination. I even later used it for a book report in the 8th grade and the teacher was quite amused with the enthusiasm evident in my synopsis. Simak is an excellent storyteller and there are so many intriguing ideas and threads. It was this book that first introduced me to the concept of a parallel world existing, not along an extra spatial dimension, but a few seconds in time behind us - like the frames of a motion picture film, just slightly different, as it was well described. A consequence of that reality would be the impossibility of time travel as there would be no independently reachable past or future. Of course, that would probably conflict with relativity theory. Anyway, a more comprehensive synopsis is given here.
My admiration was tempered a bit when I found out that the story was not originally written as a novel in 1952 but as a series of articles in a sci-fi mag called "Astounding! Science Fiction" (first chapter appearing in the issue at right), which seemed to give it a less reputable origin in my mind. Later I learned that this periodical and others helped launch what is referred to as the Golden Age of science fiction, as well as the careers of many later to be famous authors, including Isaac Asimov. Those mags were where the action was back in the 30's and 40's. Click here for a more detailed treatment. But given the original City novel was penned that long ago, it is in fact astounding how well it still holds up today, and I would still heartily recommend it to anyone.