The Three Body Problem by Catherine Shaw
This book is witten as a series of letters detailing the protagonists investigation into a series of murders set in a version of 1880's Cambridge. The protagonist, one Miss Duncan, a young school mistress takes it on herself to investigate the murder of three mathematicians, she details the events of the story to her twin sister. The background to the murders is the research of the mathematicians, and how they interact with each other.
I found this book to be a very enjoyable page-turner. I think it would be suitable for most readers.
I read this review before purchasing this book: MathFiction: The Three Body Problem (Catherine Shaw).