'In my wayward youth I figured as stock-rider, pioneer, and gold-digger in the far Northern Territory of tropical Australia. I wore the Queen's red coat and khaki as a member of the Royal North-West Mounted Police on the frontier and prairies of British North America. When the South African War broke out I laid aside my pen as a professional writer in London, took the first boat out to the Cape, and fought through all the first and the worst of the stern campaign that followed.' (The author, Preface to The Life Adventurous.)
In Australia, Mackie was a pioneer in the Gulf of Carpentaria 'on a great river, which the Dutch, in the early days, called Van Alphen, and which still bears that name on the map.' Its name was later changed to the Calvert.
Mackie wrote other novels set in Canada, western America, South Africa and the Antarctic.