Ace F-283. SF novel, part of theThe Gaston Max series which comprises The Yellow Claw (1915), The Golden Scorpion (1919), THE DAY THE WORLD ENDED (1930) - ''set in and around a fortress guarded by death rays to protect a Secret Master who plans to kill off all humanity except for surgically altered inhabitants of his new Utopia'' - and Seven Sins (1943). First published in hardcover by Doubleday in 1930, this 1964 Ace printing is the first paperback edition.of this title.