No idea what other reviewers were complaining about. Formal writing? Nonsense. The book is wonderfully written. Very easy reading, highly entertaining and elegantly presented.As a period piece, I can't find anything I would fault. Well, libraries on demonology were probably not that common, even in the Suffolk countryside, but certainly there was an avid interest in collecting arcane lore (actual or spun from moonbeams and strong wine) during the 1800s. I imagine Margery Allingham was thinking along those lines. It's a very minor part of the tale, an aside in a plot device for tying up loose ends, so I don't consider it a spoiler.As a detective story, there is an obvious parallel Arthur Conan Doyle story, though not nearly as sophisticated as this. Plenty of older stories yet exist of riddles hiding treasures. This is in no way a rehash of well-trodden ground, though. This story is original and ingenious. It has become an over-used plot device in more recent times, but you can't fault an author for the future use of a story idea.Characterizations - the characters are all vividly described, never veering off-character. The only issue I have is that the characters of Campion and Amanda are the only ones of depth. The others exist to prod the story forward. But, when you examine most novels, that is true. Very few stories have complex characterization outside the main one or two people as it is too hard to follow otherwise. Colour and texture, rather than detail, for everything around the main subject.