The description comes from the writings of our hero and narrator, one John Strasheim, full-time cobbler and amateur journalist. His reporting (a rare activity, we're told, though there are news programs on the net) brings him to the attention of the authorities. They are actually going to launch a manned mission into the Mycosystem, to investigate a new and disturbing development, the apparent ability of mycora to assimilate the microscopic machinery of the Immunity, and they want Strasheim aboard to report on the expedition for the folks back home. The idea evidently seems more reasonable to Strasheim than it did to me, and he goes along. The ship gets launched weeks ahead of schedule, owing to sabotage (!), and they're off for a few hundred pages of treachery, interviews, culture shock (from visiting remote colonies of survivors), falling through space, playing with cellular automata, ship-board blooms, and discussing just what the mycora is and what should be done about it. It's a fun ride, even if the ending manages to be both formulaic and not very sensible. [A discussion of the ending, and other spoiler-laden matters.]
It's not a white-knuckle read, nor a profound one. But it is an intelligent story with good world-building, quite free of the technolibertarian idiocy of too many stories involving nanotechnology, well-told and, at least through p. 300, well-plotted. (Someone really ought to look into why so many good SF novels end badly.) Unless conditions change drastically, it seems nearly inevitable that eventually --- maybe next century, maybe in five --- we'll start playing around with molecular machines, as active devices for changing the world, instead of just computers for interpreting it. The possibility then opens up that we'll make --- either deliberately or by accident --- something which will be very effective at turning everything else into more of itself, what those who make it their profession to speculate about such matters call ``grey goo.'' It may not happen; but if it does, McCarthy's book will all but surely prove to have been wildly optimistic.