A librarian in a low tech steam powered far future devises a vast computer to administer her city-state and wage war on unfriendly neighboring states. But the real purpose of the machine is to guide weapons that can destroy the automated sunshade that is slowly freezing Earth into a new ice-age. Two thousand years in the future, electronics are not feasible to produce, -- space based monitors annihilate any EM devices they detect. There are so many new ideas colliding in this book; I've just given you the biggest ones. The "Great Machine" is a computer made up of all humans; I believe they have some assistance from slide-rules and the like. It's an amusing notion, and actually slightly more plausible than I first supposed after some research on my part. It seems like McMullen had a notebook where he wrote down any big idea and SF plot device and after saving up for years dumped them all into this book. It's surprisingly compelling reading. The narration style and tone doesn't really match most modern novels; it's rather detached, and the pacing is all over the place. Parts of the book seem under structured somehow. Nevertheless it's well worth reading. The second book in the series seemed to be better structured.