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".

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 Pan as a useful symbol for the power of nature and paganism.