In a drunken stupor, Watson and Sir Henry decided to catch the killer. They hear someone’s howl. Sir Henry suggests that this is a dog, and the killer Selden has already slipped away. Watson noticed another man hiding in a swamp, who was also disappearing. The drunken hike brought nothing but a big hangover the next morning. Dr. Watson learns from Eliza that Charles Baskerville should have had a date on the day of his death, according to a letter from an unknown person designated by the initials L. L. This same L. L. is Laura Lyons, the daughter of old Frankland, a local hackney. Laura tells Watson that there was nothing serious between her and Sir Charles - just a wealthy landowner provided material and moral assistance to a divorced woman, as well as Jack Stapleton. Hunks Frankland gives the doctor information about a convict hiding in a swamp: a child carries food to a killer. Barrymore says that in the swamp, in addition to Selden, another person is hiding; Watson is worried that the lover, Sir Henry, is walking there, and Dr. Mortimer is losing his dog Snoopy, who escaped to a dog howl. Dr. Watson is convinced that the dog still exists. To quickly sort things out, Watson goes to the cave in order to find this person. It turns out to be Sherlock Holmes, who is also temporarily hiding in the swamps, and the child Frankland spoke of was carrying Holmes food. All this time, while Watson guarded the life of Sir Henry, Holmes made inquiries. The main suspect becomes Jack Stapleton - as it turns out after visiting the family gallery in Baskerville Hall, also a representative of the Baskervilles. It was Stapleton who set a dog on Sir Charles, as a result of which he died of a heart attack; now Jack is similarly trying to remove Henry. Baril is not a sister, but the wife of a naturalist. At this time, Selden was killed in the swamp: fleeing from a dog, he crashed, falling from a cliff. In order to catch the criminal red-handed, Holmes organizes a test that is dangerous for Sir Henry, who was invited to visit the Stapleton. Inspector Lestrade arrives at Baskerville Hall to help. In the evening at the Stapleton’s house, three would organize surveillance. Watson sees that just before Sir Henry left, he had already let out a dog - a huge dog with a phosphorus coated face. The dog attacks Henry and nearly kills him, but Lestrade kills the dog with a few shots. Stapleton’s wife says that Jack can hide only in the center of the Grimpen bog, where he kept the dog. There, Holmes discovers all the evidence: the stolen shoe of Sir Henry for dragging the dog, the remains of the dog Dr. Mortimer Snoopy, as well as phosphorus. A shot is heard, and a shootout with Stapleton begins. Fleeing the chase, Stapleton drowns in a quagmire. Stressed Sir Henry is treated by Mortimer, and Sherlock Holmes and Dr. Watson return to London, where Holmes talks about Stapleton: in fact, he is the son of Sir Charles Baskerville’s younger brother - Roger. He moved to South America, where he married Baril Garcia, a beautiful woman from Costa Rica, stole government money and fled to England, where he changed his name to Vandeler and opened a private school in Yorkshire. Desiring to take possession of the inheritance, Stapleton, having heard from Sir Charles a family tradition of a monstrous dog, “embodies” it. Sir Charles, as Stapleton conceived, is dying, but Sir Henry, who has appeared, forces him to start all over again. However, it remains a mystery to Holmes how Stapleton was going to prove his inheritance rights, but Watson does not know, and Holmes never reveals to him this secret entrusted to him, why Laura Lyons was such an obedient instrument in Stapleton’s hands.