Nightmare!

Also published as Nightmare! A Tale of Waking Terror by Francis Stevens.
Come now and see a strange island peopled with monstrous beings and carnivorous plants, on which vie two brother princes on opposite sides of a great conflict, with a woman who is more than match for either between them.
Nightmare was the first in a type of fiction that became known as dark fantasy, and remains a high water mark in the genre. First published in 1916, this debut novel began the three year career in which Francis Stevens became the person that launched entire genres of modern fictions. With her vast imagination and flair for the unusual and exciting, Gertrude Barrows Bennett created a seed that has grown into thousands of great works.
An exciting adventure tale in which "The air of mystery and the atmospheric buildup are superbly done, indicating a ranking talent." [Sam Moskowitz] Come along for a voyage on a great ocean liner to an uncharted land, filled with strange beast and secrets of alchemy, and a woman strong enough to win over them.
Gertrude Barrows Bennett is better known by her pen-name, Francis Stevens. With a career that only spanned three years between 1917 and 1920, when she stopped writing after her mother's death, she is credited as "the woman who invented dark fantasy". She was a direct influence on H.P. Lovecraft, and in the words of Sam Moskowitz was the "greatest woman writer of science fiction in the period between Mary Wollstonecraft Shelley and C.L. Moore""