I own the [regular] book " The Exploits of Sherlock Holmes." It was written by Arthur's son Adrian Conan Doyle and John Dickson Carr. You can find more
here. You can not get it as an ebook as far as I know. It is okay reading.
I am greatly interested in
The House of Silk and will be reading it once I can get a copy from my library. I hope that it can live up to my modest expectations. I tend to have low expectations of the pastiche's as I hold everything up to "The Sign of Four," which is probably the best novel I have read. It is Holmes at his best in my opinion.
I read
The Italian Secretary many years ago and it left no opinion or memory that I can recall, so I can't recommend it.