In the summer of 1921, young doctor Francis Ardan and his father are exploring the most remote regions of Upper Siam (now Thailand), when they encounter a dying man whose skin is the color of jade.
His revelations lead the intrepid father-and-son team to discover the existence of Inramonda, a secret, underground realm ruled by an immortal tyrant known as His Eternal Wisdom, whose subjects are a race of artificially created Jade Men.
He plots to seize power in Southeast Asia.