Dr. Turner's books are all out of print; in addition, both "Taken" and "Masquerade of Angels" are very expensive to obtain on the used market. They also happen to be two of the most important books ever written on the UFO abduction phenomenon.  "Into the Fringe," Dr. Turner's first book, also provides much valuable background information on the experiences of this pioneering researcher. 

Taken: Inside the Alien-Human Abduction Agenda (PDF) traduction française (not related to the television miniseries)
Masquerade of Angels (PDF)
Into the Fringe (PDF)
Also See: Barbara: The Story of a UFO Investigator by Barbara Bartholic