Miss Brown of X.Y.O. is a 1927 mystery thriller novel by the British writer E. Phillips Oppenheim. It was notable amongst thrillers of the time for its use of an everyday female character as heroine.
Miss Edith Brown, a comely typist, stumbles upon the doorstep of the dying Colonel Dessiter who has just returned from a mission throughout Europe fighting against the forces of the Communist Internationale. After she transcribes his report, she is thrust into the massive intrigue and deadly conflict between forces trying to bring about a revolution in England, and the small organization known as X.Y.O. which is defending the realm.