On Secret Service: The Secret Wireless Code

Published in Hearst's Magazine, Aug 1915. Collected as chapters 8-9 in the book The Door of Dread
While Sadie is looking forward to a private dinner with Wilsnach, she is disappointed to find they are joined by her boss, Kestner, and a man from the Intelligence Department. As they talk during their meal about their ongoing attempts to capture Spymaster Keudell and team, Sadie realizes they are being listened to via a hidden Dictaphone and that the Intelligence man is not who he claims to be.