On Secret Service: The Secret Conference

Published in Hearst's Magazine, Nov 1915. Collected as chapters 14-16 in the book The Door of Dread
Sadie Wimpel comes up with her own plan for catching Spymaster Keudell and his minions, making use of a nurse she hires named Mabel Poole and a scheme to use a Dictaphone to overhear their latest plans at a conference that she knows is going to take place.