Love the character of Keller.....he just goes along clamly killing people and he is so inventive!
There are many reasons why a book might be unavailable.
Sometimes a book goes temporarily out of print - and sometimes no audio version has ever been recorded. Audible wants to give you the most complete selection we can and we'll keep adding series and filling in gaps as quickly as possible.
I always like Lawrence B and this was a fine example of his Keller series