I get a lot of questions about the Maric series. No, I was never a member of the New Zealand SAS. Yes, Cal does exist (though of course he isn't called Cal) and he was an SAS instructor, who eventually retired and started a martial arts club. He trained me up to a Black Belt level, and we talked a lot about his time in SAS circles. His experiences have certainly made it easier for me to write about elite force ops.
This book is a complete story in itself. The series uses the same main character, plus a few others, in different locations around the world.