In The Time Machine, H. G. Wells writes about a people who lived under ground. Since their eyes were accustomed to darkness, they could not endure the light of the moon; so they visited the surface only on dark nights when it was absent from the sky.
In The Terror of Blue John Gap, Sir Arthur Conan Doyle treats a similar theme. However, while the creatures described by Wells are degenerate human beings, Doyle’s hero is a monster that looks something like a giant bear. Moreover, while the people described by Wells live in the distant future, the monster described by Doyle lives in the early twentieth century.
The setting of the story is a rural area in England. There are many caves in the area, including one that is man-made. It is a marvelous Roman construction that intersects with natural caves.
As you may recall, the Roman legions had conquered the territory where the English nation later developed. It began with two somewhat ineffectual campaigns of Julius Caesar. The real conquest was effected during the reign of Claudius. Agricola later tried to bring southern Scotland under Roman rule, but eventually gave up the project. Roman legions remained on English soil till around 410 A.D. Sometime during their occupation, the Romans built a tunnel that became known as Blue John Gap because of a peculiar purple mineral that it contained. [I am not certain whether Blue John Gap was a structure that actually existed or whether it was a landmark invented by Sir Arthur Conan Doyle for the purpose of this story.]
In addition to the monster, which was actually an antihero rather than a hero, the hero of the story was Dr. James Hardcastle. He was suffering from a serious ailment, so he hoped that a change of atmosphere would improve his health. He decided to spend time at the farm of two elderly sisters whose surname was Allerton. Their farm was located near Blue John Gap.
The cave was the object of local superstition. Weird sounds occasionally emanated from its interior, and nearby sheep occasionally disappeared during the night. It was commonly believed that some monster lurked within.
Hardcastle learned about these beliefs while he was standing at the entrance of this manmade tunnel. A young man named Armitage happened to see him and warned him about its dangers. Hardcastle did not believe him.
After exploring the cave himself, Hardcastle changed his mind. He entered the Roman tunnel with candles and matches. After turning off into one of the intersecting natural caves, he fell into some water. His candle went out, and his matches got wet. Since he could not find his way out in the dark, he had to wait till his matches dried out so that he could light another candle.
While he waited in the dark, he heard footsteps approaching. Then some animal began to lap up water. The animal came dangerously close to him, but eventually retired.
Hardcastle did not want to enhance the superstitious tendencies of the local residents by telling them about his experiences, but he confided in a learned man named Dr. Mark Johnson.
Dr. Johnson said that he was not qualified to comment on the story. Instead, he referred Hardcastle to Mr. Picton of Castleton. Before entering Picton’s shop, he asked a neighbor for information about the illustrious man. He learned that Mr. Picton was an excellent “mad doctor” and that his asylum was located nearby. Needless to say, Hardcastle decided not to tell his story to Mr. Picton.
Later, several sheep disappeared on cloudy and moonless nights. Worse yet, Armitage disappeared. People thought that he had left the area, but Hardcastle suspected that he was another victim of the monster of Blue John Gap. As a result, he decided to tell his story to the police. The police did not believe him.
In spite of his infirmity, Hardcastle was a brave man. He decided to face the monster himself. He bought a lantern and a rifle, and lurked about the cave on a cloudy night. He shot at the monster and followed it into the cave. However, the monster surprised him and knocked him unconscious.
Fortunately, he had left a note telling the Allertons where they should look for him in case that he did not return. A group of people found him and brought him back to the farm.
Many learned people still doubted Hardcastle’s story. They cited his ill health as a probable cause of his hallucinations. Others wished to explore the cave to find out the truth, but this proved to be impossible. When the local residents heard the story, they believed it and blocked up the tunnel with large boulders. Henceforth, no one could enter, and no monster could get out.
To write these notes, I consulted an online version of the story presented by Project Gutenberg.