This story begins with an adventurous yet ill-prepared explorer lost in a cave after having made the poor decision to split off from his tour group. He soon discovers he is not alone, and his mind races at what sort of ferocious oddity of nature must live in such a secluded atmosphere, cut off from all sunlight and contact with the outside world. It's not long before his torch sputters out and he is left in complete darkness, wrestling with his own imagination and the frightening sounds of the unseen beast shuffling toward him.
No spoilers, but I will say that it's one of those twist endings that might at one time have shocked readers, but by today's standards is rather predictable. It's like if someone were to watch Hitchcock's Psycho for the first time today. Set against its modern contemporaries, how much would Psycho, a complete mindfuck in its day, surprise anyone? No one. It's still a valuable piece of the American/English film heritage, but it no longer holds the same power for today's jaded audiences. A few of Lovecraft's stories in this collection suffer from that same peril, and "The Beast in the Cave" is one of them.
Bearing in mind, though, that Lovecraft was only 14 years old when he wrote this story, it is an incredibly well told tale, and thankfully not too cryptic in its construction. It is sufficiently exciting, propelled on by expertly (yet by a novice) drafted descriptions of the story's setting and atmosphere, as well as the wild meanderings of the main character's imagination and memories.
Consumptive: noun | a person with a wasting disease, especially pulmonary tuberculosis | ex. During a tour of the primitive village, we came across the hut where the tribe's consumptives go in their final days.
Salubrious: adj | health-giving | ex. After spending my whole life in the smog of urban California, the salubrious Colorado mountain air was a welcome change.
Prognathous: adj | having a projecting lower jaw or chin | ex. When it attacked his puppy, Jerome kicked that prognathous, antagonistic American Bulldog right in its massive underbite of a mouth.