On the dedication page Kirk says that this "Gothick tale [is] in unblushing line of direct descent from The Castle of Otranto." Well. Authors are allowed their hyperbolic dedications, aren't they? The novel owes more to Edgar Wallace, Sax Rohmer, and even Guy Boothby but the only thing "in direct descent" from Walpole's masterful Gothic thriller is the creepy castle of the title. Nothing else.
The story starts off very much like a Gothic and there is a lot of legend and lore filling the pages, but after a rather protracted exposition (in which our hero attempts to get to the remote and unfriendly island of Carnglass at least four times) the hero does indeed arrive only to discover that the island has been taken over by a gang of thugs and criminals under the leadership of Dr. Edmund Jackman. The novel ceases to be a Gothic at this point and transforms into an adventure/crime novel.
It's entertaining and often gripping, but in the end all very familiar. Even the supernatural elements are rationalized. I was disappointed by that since at one point they seemed very other worldly. Not at all in line with Walpole, Radcliffe or any other genuine Gothic writer.