Level 6  (Ledbetter, 2020) - This text is only available as an audiobook. It's a sequel to Level 5, which similarly was only in audio format in what is now listed as the Killday series. I met the author, William Ledbetter, during a convention in Houston a couple of years ago. We were both panelists for writing discussions. One thing I love about Ledbetter's work is the science fidelity