A variety of groups with diverse aims, but an overlapping desire to end modern technological society (which they call the Big System), create a nanotech plague ("Daybreak") which both destroys petroleum-based fuels, rubber and plastics and eats away any metal conductors carrying electricity.
An open question in the book is whether these groups, and their shared motivations, are coordinated by some conscious actor, or whether they are an emergent property / meme that attained a critical mass.
A shadowy neofeudalist group (the "Castle movement") led by a reactionary billionaire may be inadvertent saviors of society... or may have some deeper involvement in things.
[1] Russell Letson Locus called it "one of the most absorbing" novels he had read that year and that the title alludes to a "hard-SF-style treatment of some notions that in other hands might have been just literalized metaphors, but that here become frighteningly concrete.
"[2] Kelly Jennings of Strange Horizons wrote: "The strengths of the book—including its large cast, political intrigue, ideas, sense of landscape and pace—are many.