Very complex, yet has an intriguing symmetry to it. As long as you’ve read the prior novels in the series, of course. Otherwise, the reader can’t really “get” all the references to earlier characters, parallels, names, places, etc. that are key to solving this mysterious adventure.
BTW, I still think Rafferty & Thomas should have their own completely original series, without Holmes & Watson involved at all. I’d sure read/buy it!