Dead Man' s Folly by Agatha Christie

A boring book...I don't know if it's because I read a lot of modern thrillers but this one is really old fashioned.
It's strange, because until now I had enjoyed all of Agatha Christie's books.
Perhaps it's only that one which is not good...

The only interests are the fact that in the story appears a writer of detective stories, and we are comfronted to the way her mind works when she writes a book ( it is Agatha herself describing her own way of working?) the second being the disppearance of one of the characters, like Agatha herself disappeared once in her life?
And all that stands place in Devon...

Perhaps, the book is too personal... That might be its problem..Writers of detective stories need some distance, don't they?