It is a young girl's diary, in which she describes in ingenuous, evocative prose her strange impressions of the countryside in which she lives as well as conversations with her nurse, who initiates her into a secret world of folklore and black magic.
The girl's tale gradually develops a mounting atmosphere of suspense, with suggestions of witchcraft, only to break off abruptly just at the point where a supreme revelation seems imminent.
In a return to the frame story, Ambrose reveals that the girl's body was later found dead near a seemingly pagan statue in the woods.
E. F. Bleiler wrote that the narrative in the Green Book "is probably the finest single supernatural story of the century, perhaps in the literature",[7] and Michael Dirda has stated: "If I were to list the greatest supernatural short stories of all time, I would start with Arthur Machen’s 'The White People,' about a young girl’s unknowing initiation into an ancient, otherworldly cult.
The story has also served as the inspiration for T. E. D. Klein's novel The Ceremonies[11] and may have been an influence on the plot of Guillermo del Toro's film Pan's Labyrinth.