The Black Secret (1919)

Moving stealthily in the background, always keeping their tracks well covered, the perpetrators of the terrible Black Secret conducted heir campaign with Michiavellian ingenuity.

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"