Fallen Angels is a collaborative effort between Larry Niven, Jerry Pournelle, and Michael Flynn. In a nutshell, it is a celebration of fandom. Sure, it has an interesting plot, with Earth experiencing an ice age in no small part due to radical environmentalists taking over the government and banning the development of technology, but really the book is about fans.
Ok, so there’s an ice age on Earth (as previously stated). It was caused by the periodic cooling of the sun (which is apparently a real, cyclical phenomenon, so we might need to start stocking up on the furs) combined with those pesky radical greens taking control and passing such strict laws against pollution that the amount of particulate matter in the atmosphere dropped significantly. This caused a reduction in rainfall, which caused a reduction in cloud cover. The lack of cloud cover meant the earth couldn’t retain heat as well, and so the cooling. That’s the science.
Before all space programs were shut down, 2 space stations were established, and when Earth’s governments went all Luddite, they broke contact and have since been scraping by on recycled everything and occasionally scooping nitrogen from Earth’s atmosphere. On one of these missions, two pilots in a ‘scoop ship’ are shot down by the United States (I think) government, which blames the scoop ships and ‘air pirates’ from the space stations for the ice age.
Enter fandom. A group of dedicated fans put together a rescue mission to save the pilots, who they call Angels because they are from the space stations orbiting above the Earth. The fans are part of an underground movement in favor of science and technology and, of course, science fiction. The story mocks radicalism in several forms, and takes aim at a a few specific politicians also. But mostly it celebrates what a bunch a geeks can do when they put their minds to it. It is a great book, and anyone who has ever been to a con (or thought of going to one, or even heard about them) should read it.