I'd do nothing but reading if I could (ok, maybe eat some great food, buy some fancy shoes between two books...oh, and spend some quality time with the gorgeous guy I married while I am on reading-break anyway...)
I pretty much guessed who might be the culprit after 50%.
Not because of real clues, more because of the structure and the characters.
Mrs Christie pulled one, that she had pulled before:
So I hate to say it, but I discovered a pattern...