This is actually two books. Part I (1-223), titled "Underground" (Andaguraundo) was published in 1997; Part II ("The Place that was Promised") was written and published separately the following year.
Part I consists of interviews with the victims (see updates; this section is too long and is tedious). Part II consists of interviews with members and former members of Aum Shinrikyo.
And this is where things get really weird....
The members of this cult -- who resemble a cross between the Moonies and Lyndon LaRouche -- are uniformly described as ordinary (read: "mediocre") Japanese who were nonetheless interested in the "deeper" problems of life. All of them describe feelings of alienation -- of feeling that there was "a hole in them", something "incomplete". Murakami points out, in one of these interviews, that adolescents who get interested in the question of meaning, usually start reading books -- philosophy, and so forth. But these individuals report that they were not readers. They simply relied on their intuitions....
Aum held to what is known as Vajrayana Buddhism -- which, inter alia, suggested that murder can, in the hands of the enlightened, be a "fast path" to salvation -- (that is, for the salvation of the murderer...)
Murakami's point in all this, is that we should study these individuals not to find out what "they" think -- but to cast a reflected light back upon "us" -- the society (Japan's) that produced them. As he says (229):
"Or rather, 'they' are the mirror of 'us'.... Now of course a mirror image is always darker and distorted. Convex and concave swap places... light and shadow play tricks. But take away these dark flaws and the two images are uncannily similar... Which is why we avoid looking directly at the image, why, consciously or not, we keep eliminating these dark elements from the face we want to see. These subconscious shadows are an 'underground' that we carry around within us, and the bitter aftertaste that continues to plague us long after the Tokyo gas attack comes seeping out from below."
A strange book.