A discussion between two men on the nature of evil leads one of them to reveal a mysterious Green Book he possesses. 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. Throughout, the girl makes cryptic allusions to such topics as "nymphs", "Dôls", "voolas," "white, green, and scarlet ceremonies", "Aklo letters", the "Xu" and "Chian" languages, "Mao games", and a game called "Troy Town". 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, the diary's custodian reveals that the girl's body was later found dead near a seemingly pagan statue in the woods. He adds that she had "poisoned herself—in time", making the analogy of a child finding the key to a locked medicine cabinet.