Kings & Queens of England and Scotland by Plantagenet Somerset Fry is a 96-page concise reference book about the monarchs of England, Scotland, Great Britain, and the United Kingdom. Though is primarily focused on the monarchs of England (and successor unions) with each ruler getting their own individual article from 1066-to-present, while the Scottish monarchs were only briefly covered in comparison. Not all the information given in monarch articles is correct, at least to those readers well versed in history, but overall the book is a good reference book.
New on the blog - my meanderings about the Tudors being Beauforts.