The book documented the adventures of a female humanoid being whose body was altered to enable her to be a message/document carrier as well as a highly trained military-esq operative when needed for an organization. One of these alterations was a concealed pouch within her own body where she could hide away secret documents and the like.
Though her line of work heavily discouraged close contact with other people, the story explored her experiences and conflicts in developing relationships. It also detailed her experiences and feelings being a top secret message runner and her internal struggle with being who she was/is and having that secret pouch.
I can't distinctly recall the setting of the story; beside the fact that the female character in question was normally always on the move (carrying and delivering the documents and protecting them at all costs), there seemed to be a mix of older/current history along with science fiction elements.