I just had to say a few words about Agatha Christie's Secret notebooks by John Curran. If you are interested in Agatha Christie then this really is a "must have". John Curran was granted permission to go through all Agatha's notebooks - she used children's exercise books to plot all her mysteries and write down notes and ideas as they occurred to her.
John has done a really brilliant job in putting this book together and it is interesting to read Agatha's notes and to see the things she put in the books and the things she omitted. Probably best to read this once you have read Agatha's books as there are spoilers.
What I particularly like about this book is the fact that there are facsimile pages of Agatha's notes and next to these they are transcribed so very easy to read. Its absolutely fascinating and gives an insight into how the Queen of Crime plotted her mysteries.