The Black Secret.

Adventures of an American Secret Service-girl in search of an important German secret during the war. Chapters: [1] “The Great Secret,”; [2] “Marked for Death,”; [3] “The Gas Chamber,”; [4] “Below the Waterline,”; [5] “The Acid Bath,”; [6] “The Unknown,”; [7] “The Betrayal,”; [8] “A Crippled Hand,”; [9] “Woes of Deceit,”; [10] “The Inn of Dread,”; [11] “The Death Studio,”; [12] “The Chance Trail,"; [13] “Wings of Mystery,”; [14] “The Hidden Way,”; [15] “The Secret Host"