The first novel by Natsuhiko Kyogoku, and the one to which Mouryou no Hako is a sequel.
The prose is rendered nicely into English, while retaining some of the stylistics tics of the original (no sentence broken between pages, at least for the first 200-odd pages); there are a few translators notes where allusions are made to various folk-tales. The most obtrusive translation quirks are where dates are concerned
The book he was reading was something from the Edo Period [1603-1868]...
but those are quickly past after the opening chapter.
Many of the cast of Mouryou no Hako appear in this first novel -- many more than I had expected. And Kyogoku seems to have a thing about bizarre hospitals.
By the end, this is clearly a strong first novel -- and it's also clear why the next book he wrote about the same cast was the one that got the adaptations : this one relied just a bit too much on the power of coincidence (three different characters suffering the same hysterical blindness, for one), and on having some of the main cast involved at some point in the past with one or other of the major players in the mystery.
Still, if you enjoyed the Mouryou no Hako anime, this is the nearest thing you'll get to having another fix of the same in English language.