The story was excellent but the narrator sound like either on microphone or inside a tin can.
This is one of my favorite series. The Plague Within has a compelling premise and the story delivers.
I always enjoy a medical mystery. Makes even the doctors and nurses that take care of us appear human. Some times in person, they don't.
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.