The first three quarters of this book kept me fairly gripped and I was keen to find out the solution to the various mysteries. As it approached the end, however, it became somewhat silly, with some giant plot holes. I don't want to give spoilers, but perhaps I might mention that telephones have never run on mains electricity, and that even if they did, a power cut in one town (before the National Grid) would not mean that the only way to communicate would be a long drive. What schools have ever been in session between Christmas and New Year? The revelations of who's who depend on unlikely coincidences of a Dickensian nature.
The author has strange quirks. Hot chocolate (in fact known as cocoa in the 1920s!) and hot baths are particular obsessions of his. Food and drink of all kinds play an extraordinary part, even when of no relevance. For some reason, he doesn't seem to know the word "hymn". The church services he describes have "songs".
The main problem with the book, however, is the author's general lack of knowledge of the 1920s. If you are going to set a book in a bygone period, surely a bit of research, or at least checking, is in order. Teabags? "Exotic" coloured underwear for boys? A hardware shop where the customers wander around with items from the shelves? Young people calling unrelated adults by their first names? Respectable women casually saying "Jesus Christ" in conversation without anyone turning a hair? If we look at some of the other turns of phrase, it starts to become laughable. People greeting each other with "Hi", "What are you like?", "between a rock and a hard place", "we better", "this new technology", etc., etc., etc. (There are also quite a few basic grammar mistakes).
There's a reason why books are offered for free.