In The Nyctalope vs The Antichrist (1927), the indomitable Leo Saint-Clair, a.k.a. The Nyctalope, faces his greatest foe ever: Leonid Zattan, evil incarnate, Prince of Issyk-Kul, a secret kingdom kocated in central Asia. Leo is drawn into a merciless struggle between two worldwide organizations: one serving Good and defending the established order, led by the wise kabbalist Mathias Lumen; the other serving Evil and aiming to overthrow the governments of the world in order to take advantage of the resulting chaos and seize power, led by Zattan and his ally, the Red Princess, Diana
Ivanovna Krasnoview, Queen of the Hashishins. Victory depends on the fulfillment of a Nostradamus prophecy that predicts the coming of the Antichrist, who can only be defeated by the marriage of a "Golden Virgin" (the wealthy heiress Sylvie MacDhul) to a new Messiah.

The Nyctalope vs. The Antichrist is a pivotal novel in the series. In it, Leo meets the man who will his best and most loyal adviser, Gnô Mitang. He marries Sylvie, who will give him a son, and founds an international crime-fighting organization to ensure the world's safety.