This is the third novella in the intriguingly disparate Gem Universe series, in which the magical power held within gems in a particular valley shapes the rise and fall of different civilisations over centuries. The Jewel and Her Lapidary, the first book in the series, dealt with the fall of a monarchy built around the power of gems. The second, The Fire Opal Mechanism (review), is set a long time after and a long way away, in a city where human knowledge is under threat from a technology which destroys unique books and reproduces the information in them in a single, approved form. This time, the action is once again centred around an academic institution, at a point where society has effectively forgotten that "real" gems once held power and built its technology around synthetic alternatives. The Valley where gems originated is now a marginalised backwater, its inhabitants nominally given ownership of their own cultural artefacts but subjected to outside study and interpretation of their history.
The action of the Book of Gems follows two women. Devina, or Dev, is a researcher and descendent of a Valley family, returning on a trip to locate her missing supervisor, who stole Dev's research and then disappeared after a series of increasingly fragmented and cryptic messages back to the university. Lacking support from her university and cautious about revealing her own family history, Dev soon meets with her cousin Lurai, who is trying to make ends meet running the Valley's main inn after the disappearance of her mother. Lurai's mother, it transpires, was hired to guide Dev's supervisor into the ruins of the Palace of Gems - which outside researchers are forbidden from setting foot in - and so the two women's goals quickly become intertwined, particularly as the gems themselves start making themselves heard. And so does the entity calling itself the Prince of Gems...
While this novella could technically stand alone, The Book of Gems really benefits from an understanding of the Gem Universe and the magic which Wilde has built up over the series. Even with the technological advancement over the course of the books, the Valley's gems remain fundamentally mysterious and unknowable: magical artefacts with their own voice, offering power which comes at an often horrifying price, demanding strict control from those who harness it. (In other words, the tropes are on point). It helps that we only see this world in glimpses, through novellas and shorter fiction, with the advancements between each story left largely unexplored. While I'm sure Wilde has the storytelling ability to pull off a longer novel in the Gem Universe, this is the type of world where catching glimpses creates a very... satisfying... sense of being unsatisfied. (I note, on rereading my 2019 review of The Fire Opal Mechanism, that I didn't feel this way then... but I do now!)
The Book of Gems also offers a sense of balance to the revolutionary upheaval that we saw in The Gem and Her Lapidary, and a literal excavation of the legacy that was buried in that book, although I am more ambivalent about the political direction here. Because the Gems are linked to the Valley, a location which has been subsumed and marginalised by the larger Republics which have come after, there's a direct link between their lost magic and the lost independence of the Valley itself. The direct influence of the Republic isn't present - not in the same way as The Fire Opal Mechanism, but the power of colonising forces is well represented through Dev's university, which sends researchers into the Valley to interpret the artefacts which its own people are tasked with digging up. That the university refuses to allow Dev, a descendent of the Valley, the status to pursue her own work, and maintained a system where her supervisor was able to take it from her without the intervention of any of her colleagues, is icing on the cake. It makes Dev more sympathetic, but the extractiveness of the institution is well established even before Dev (and Inara's) personal grievances come into play.
The alternative, however, is presented (alongside a gauntlet of increasing body horror) as a return to rightful monarchy, and that too feels... off. Perhaps this is the point at which the sparseness of the Gem Universe setting becomes a drawback rather than a benefit: it feels like the time we spend with Dev and Inara never quite gets us to a point of understanding how people in the Valley feel, other than a general disdain for their research visitors. While novella length is tricky when it comes to political deep dives, I would have liked to see more nuance behind the presentation of a returned monarchy and what that might mean for the Valley: sure, there is a cultural memory of Gems and a lost past which makes uncovering it attractive, but does the reality line up with that cultural memory? The Book of Gems glosses over that for what feels like an easier "Isn't reconnecting with one's heritage great" ending, and I don't think that does the rest of the book justice.
Still, this is a great series, and there's lots in The Book of Gems to enjoy, particularly if you derive enjoyment from squirming over weird magical body alterations and/or shitty academic practices. This series has been billed as a trilogy, and there's certainly a sense of completion here, but thhere's also short fiction in this universe so perhaps this isn't the last time we'll see the Gems and the Lapidaries of the Valley, and their creepy singing rock "friends". Perhaps they'll institute a more representative form of self-governance in our absence? You never know.