You walk into the room and it is like stepping into the grand library. Wall to wall and floor to ceiling is taken up by leather bound loaded bookshelves. All of the tomes are in varying states of decay and none of which are new.
Victorian Ladies used to use their decorative fans to communicate simple messages to their lovers while chaperones or husbands watched. These messages include "Yes", "No", "We've been discovered", "When can I meet you", etc. An Assassin's League of women could easily use this secret language to their advantage, sending messages to each other in hopes of reaching their target at a crowded ball.