I think I can sum up this book in one word: dire.
I can't find a single redeeming feature. Christmas hardly comes into it. The sole Cotswold aspect is mentions of Cirencester and Cheltenham plus a few Mummersetshire accents for the common folk (who are, of course, mostly half-witted). The writing is abysmal. I lost count of the number of times we were told the main character Mrs Bradley 'cackled' or 'leered' - I'm not sure the author knew what these words meant. Certainly they don't make her seem appealing. None of the characters ever becomes more than a cardboard cutout. The plot is poorly thought through, and for page after page everyone is convinced about who did it (there are very few suspects), but struggles to do anything about it. And then it turns out they did do it. The whole experience seemed far longer than it was.
I'm not going to tell you how to buy this book - it's not even 'good' bad. It's just not worth reading.