In order to fully appreciate this book you need to read the previous books in the Shonak Series.
The Shonakians are a simple, placid race of people but so different from us that a great deal of background is provided in the first book, The Crown of Happenstance. The book introduces the three main protagonists in the book; Bon of Shonak, Itself the over spirit of the "Six Earths", and Atsa, a proto-Hopi and all around honest, caring, spiritual human, with profound interests. This is where you learn about Shonak, and its people, about their phase altering technology, about their thirst for intellectual and technical conquest, and about their love for Earth-watching.
The next book, It's About Time, discovers a new relationship between Earth and Shonak. Itself causes an otherwise inexplicable time shift that propels Earth 3210 years into its future while there is no time-change on Shonak. Because Earth is now an advanced, technological world, Shonak introduces itself to them. They do not reveal their invasion of privacy on Earth, which has turned the planet into a virtual zoo for Shonak's voyeuristic pleasure, but they do think they owe Earth something for it. They offer their assistance in areas of crime control, better agriculture, using ocean water for crops and drinking, cleaning the oceans, etc. All the while Shonak continues to expand its surveillance of everyone and everything, everywhere, using their massive fleet of surveillance bots, some of which look like rocks or trees, while others look like beetles, birds, dogs and cats, and people, among other things. The human-looking bots are perfect in every detail and are known as humbots. There is a scandal over the humbots, once Earth discovers them, and this causes some issues between the planets.
Book Three contains a series of bot-collected vignettes of Earth behavior prepared for young students in their final quarter of their forty-year education. These people live beyond 1600 years so forty years of schooling is not a significant issue, and there is much to learn before they can join adult society on their own. These vignettes are designed to prepare these young, pre-adult Shonakians for their long life of vid-watching. Every Shonakian enjoys watching the very different people of Earth go about their complex, difficult, conflicted lives and join Vid-Watch clubs that specialize in different aspects of life on Earth.
Book Four shows how Earth catches us to Shonak in terms of their most impactful technologies; phase change and anti-gravity flight. Earth also develops a way to detect every kind of Shonakian surveillance device, from the rock to the human, and they are amazed and unhappy to find the true extent of their integration in human society with over a million humbots. They have many millions of static collection devices and countless animals and insects all designed to watch and record and show the multitude of Shonak's Vid-Watch clubs. While Earth has known that they collect video and audio of life on Earth they had no idea how large an effort this had become. But rather than destroy these devices or ban them Earth decides that there is money to be made from this situation. They decide that if Shonak wants to watch Earthers they can pay for the privilege. It's payback time!