Any story where Mani character is part of or invited into a secret society.
Give my Love to Rose, by Scotland-the-Brave, if I remember the story correctly. Perhaps read the Romantic Vigilante first, to get familiar with the characters.
Try K2 by gwresearch. Long, pretty fun, occasionally silly adventure with NAZI & Knights Templar treasure, spies, the fate of the world, a porn star driving a tractor... something for everyone.
My protagonist in Agatha Allbut & The Bimbo Squad joins a skull and bones type secret sorority, well except that it's all about sex.
My stories:
The Vault: https://storiesonline.net/s/47915/the-vault
Jennifer: Inner Circle: https://storiesonline.net/s/19205/jennifer-inner-circle
SigEpChi https://storiesonline.net/s/47524/sigepchi
Among others.