Novel by Lauren Scharhag and Coyote Kishpaugh. It is the second in the series featuring the Order of the Four Sons (the first volume being The Order of the Four Sons) and their battle against the enemies of humankind.
Blurb from the book's Amazon.co.uk page :
The Order of the Four Sons, Book II follows the team -- JD, Murphy, Doug and Kate -- as they pursue Bathory across the face of a hostile world known as Carcosa. Director Clayton Grabowski and the Oracle find themselves mired in the political intrigues of the Order's leadership, while back on Earth, Bill forges an uneasy alliance with a government agent. As they race to recover the Wand of Deleth, they uncover truths they had never expected about their enemies-- and themselves.