A strong piece of work with a likeable protagonist, the self-doubting centaur Simarron. Cast out of his herd, he's come to the city (where centaurs mostly do manual labour) to work as a magical safety inspector. I love a fantasy civil servant, and I also like centaurs, so this was immediately a couple of points in the book's favour.

Simarron isn't supposed to be investigating the murders of a couple of alchemists, but he keeps feeling that it's his duty (he's very dutiful), and risks his job - which means a lot to him - rather than walk away from helping others. I liked him for that, and for his openness to befriending the other characters, even though they were very different from him and not without their annoying individual quirks. These did help to distinguish them from one another, though I found myself looking up names sometimes to remind myself who someone was; making the characters more memorable is an aspect that could be strengthened.

There are some other minor flaws. For example, there's an oddity of timing. At one point, Simarron casts doubt on the idea that the castle of the title might be developed as a resort because it takes a couple of hours to get there from the city. But later, he and a friend take from before lunch until nearly sunset to get to another part of the city - admittedly, it's winter, and we don't know how far north it is, but it still seems like across the city is further than out to the castle.

There was also a scene where a murder suspect was being interrogated, not in a closed room, but in what seemed to be the foyer of the police station, in front of a reporter and the main character. That seemed like an odd place and situation to use to interrogate someone.

Editing is mostly good, apart from the occasional place where I felt the past perfect tense was missing, the use of "may" where it should have been "might" (not every time, but sometimes) and a couple of minor and subtle vocabulary slips or poorly phrased sentences. I had a pre-publication version via Netgalley, and I will provide feedback to the publisher, so these may be resolved by time of publication.

In terms of worldbuilding, there's a bit of "Aerith and Bob," the use of this-worldly names and made-up fantasy names mixed together (sometimes a this-worldly forename and a made-up surname, sometimes a forename and surname that are both from a particular this-world ethnicity) with no apparent plan or consistency that I could make out. But the way the magic system works is, if not presented with full Sandersonian rigor, at least given enough detail that I gained a feel for what it could do. It mostly wasn't what the plot was built on or how things were resolved.

The mystery aspect is solid, with a fully developed mystery plot, not just a gesture in the direction of one like I sometimes see. There's no romance; Simarron notices the attractiveness of several people he meets, but doesn't do anything about it, and given that he's a centaur and they're not, that avoids a world of possible complications.

All in all, a capable piece of work, and the start of a series that I will be keeping an eye out for. The best thing about it is the main character, but it's also well plotted and does a decent job with the worldbuilding.