The titular characters are clones of the wife of a Balkan warlord. Seven were born, but in the chaos of war only four survived, each one picking a different role. They each have enormous hatred for each other, but the origins of this hatred are not explained. Given Sterling's inability to create narrative interest in his characters this is probably a good thing. However, his depictions of this hatred are melodramatic and do not fit with the personalities of the Caryatids.
The book is divided into three chapters, each from the life of one of the four sisters. Each chapter takes place in a different one of the world powers: the Acquis devoted to building a bright new future, the Dispensation devoted to spectacle and manipulated by a shallow ruling class, and China, the last surviving nation state. Each chapter is a portrait of life in the respective society, followed by action advancing the main plot.
Technological marvels are the main draw of any Sterling work, and they are here in spades. From neural interfaces to lightbulbs that make flesh transparent little of this is new, but the social reactions to technological change are equal parts geek and Luddite. Indeed, there is little wrong with Sterling's depiction of the world, modulo the convolutions his characters go through to support the plot.
The main plot is the scheming of a man known as Montalban to bring the Caryatids together. But why this is necessary, or what happens afterward, is never really discussed. The Epilogue offers more questions then answers, and many characters vanish, despite having been promised major roles. The plot introduces so many subplots in need of resolution that the publisher could have titled the book Six Novels in Search of an Author.
Anyone looking for unity of form or a deep novel of ideas should look elsewhere. But for all its flaws The Caryatids is fun to read.