Superior to the first volume in several respects, this installment does shed some additional light on the central mechanism of the setting, the supernatural master/slave relation, thus remedying one of the principal defaults of the first volume, which withheld information on this point, perhaps in an attempt to generate mystery and suspense that simply came across as coy.
This central mechanism is kinda cool insofar as it is platonist Forms taken literally and made manifest in the setting. (RSB and mieville do the same with more modern philosophical bits.) The platonist Forms naturally enough do not like being reduced down to material things, with limited perspectives, restricted consciousness, memory; the platonist Form made manifest has desires (typically the nihilist's desire for self-abnegation)--which desires indicate an absence, a lack, objet a, &c., something perfectly material and non-ideal--a corruption of the platonist Idea, for which suicide is the only remedy. It is what happens when Parmenides is combined with Heraclitus, but instead, as in Plato, merely on paper, here it's in a person--a nasty psychomachia, and the writer is to be commended for thinking through it. The most moving moments in the narrative typically involve the supernatural slaves.
The coolness here, however, continues: the platonist Forms are not typically engines of war (no high DPS ticking AoE WTFLOLBBQ!!, &c), but are used for economic purposes (volume I saw the platonist Form made manifest for intervention in the agricultural & manufacturing of textiles; this volume has it used for mining). There is apparently plenty of belligerent potential here, with some menacing hints about the deep history of the setting--but the violence is kept toned down.
Otherwise, a fun read. Will continue to volume III.