My children enjoyed all these Nancy Drew audiobooks. Good for about age 11 and up.
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.
This is a great story but the narration is unofrtunate and kind of irratating. I enjoyed the books narrated by Laura Linney much better.