An old friend of Dr. Warthrop's comes asking for help to track down Warthrop's colleague, the sociopathic Dr. John Kearns. At first, Warthrop is reluctant to help--until he learns that Kearns may possess information leading to a creature widely regarded as the Holy Grail of monstrumology: an organism so rare and elusive that it has never been killed, captured, or even observed in the wild. Dr. Warthrop can't resist the challenge, and soon he and Will Henry are off on another hellish quest, this time to the bizarre island of Socotra, home to some of the strangest flora and fauna in the world. And it's on Socotra that Will Henry comes face-to-face with the most horrific creature yet--and he just may pay the ultimate price for his master's ambition.