The Great God Pan by Arthur Machen

"The Great God Pan" is a novella by Welsh writer Arthur Machen. A version of the story was published in the magazine The Whirlwind in 1890, and Machen revised and extended it for its book publication (together with another story, "The Inmost Light") in 1894. On publication it was widely denounced by the press as degenerate and horrific because of its decadent style and sexual content, although it has since garnered a reputation as a classic of horror. Machen’s story was only one of many at the time to focus on the Greek God Pan as a useful symbol for the power of nature and paganism. The title was possibly inspired by the poem "A Musical Instrument" published in 1862 by Elizabeth Barrett Browning, in which the first line of every stanza ends "... the great god Pan."

Clarke agrees, somewhat unwillingly, to bear witness to a strange experiment performed by his friend, Dr. Raymond. The ultimate goal of the doctor is to open the mind of man so that he may experience the spiritual world, an experience he calls "seeing the great god Pan". He performs the experiment, which involves minor brain surgery, on a young woman named Mary. She awakens from the operation awed and terrified but quickly becomes "a hopeless idiot".

Years later, Clarke learns of a beautiful but sinister girl named Helen Vaughan, who is reported to have caused a series of mysterious happenings in her town. She spends much of her time in the woods near her house, where a young boy stumbles across her talking to a strange man one day; the boy becomes hysterical and later, after seeing a Roman statue of a satyr's head, becomes permanently feeble-minded. Helen also befriends a neighbour girl, Rachel, whom she leads several times into the woods. On one occasion Rachel returns home distraught; afterward, she returns to the woods and disappears forever.....That is all we can tell right now, it might be a spoiler.