"Mary Reilly" writes in the first-person, and she is a very charming, likeable girl (as Dr. Hyde agrees) as a narrator. As in "Alias Grace" (Margaret Atwood), I also liked reading about the life and thoughts of a Victorian/Edwardian-era servantgirl, with her difficult, dangerous (I mean household work was harmful and dangerous), unquestioned, unresented, and dawn-to-dusk working life. Of the "alternative history" genre (cf. Gregory Maguire) of the last ten years or so, that I also enjoy so much.
Dr. Henry Jekyll was a kind and sensitive gentleman, his Victorian English household well ordered and safe. Mary Reilly, his maid, worked hard, noting in her diary the deep satisfaction she took in her service to him. But Dr. Jekyll began lingering too long in his laboratory, pursuing experiments into realms Mary knew well-and prayed to forget. Then a stranger entered their lives, uncontrollable and bloodthristy, stirring dim, longhushed desires. Buried terrors were surfacing, this time to triumph and, perchance, to consume Mary in their pitiless, heartrending embrace.