The story begins with Sherlock Holmes and Dr. Watson; in his office in London. They examine a cane left in the office by an unidentified visitor. The arrival of Mortimer who presents them with a document, dated 1742, revealing the legend of the Baskerville curse. Hugo Baskerville made up with a local girl, whom he kidnapped. The girl escaped and Hugo makes a deal with the devil and sends his bloodhounds to search for her. His friends find their bodies. Since then, a beast has haunted the Baskerville family. He had just killed Charles Baskerville. Mortimer came to ask what to do about Henry and mentioned Charles’s brother Roger, who is believed to be dead. Henry had been warned by an anonymous note. Then Henry claims that his boot was stolen. Holmes suspects someone is following him, and he’s right. Henry’s decision to go to Devonshire prompts Holmes to send Watson as well. The group runs into the police, looking for an escaped con man. Watson hears a woman crying that night. They ask Barrymore about it. Watson discovers that she is lying. He learns that the telegram was delivered to Mrs. Barrymore and her husband claimed to be upstairs.
Mr. Stapleton appears, calling Watson by name. Stapleton points out the danger of the place, mentioning the mud. Watson then meets with Miss Stapleton. Believing he is Henry, she tells him to go back to London and not say anything to her brother. Later, after learning that he is Watson, she tells him to forget her warning and tries to convince him that she was worried about the curse.
Watson reports on the getaway scam, which no one has seen for two weeks, and on the relationship between Henry and Miss Stapleton, and that Mr. Stapleton seems unhappy about it. He mentions meeting Mr. Frankland from Lafter Hall. Watson recounts how Barrymore confesses that he himself did not receive the cable. He is awakened by footsteps outside his door and someone sneaking down the hall. Watson suspects that he is having an affair, which would explain his wife’s crying. Henry’s affair with Miss Stapleton causes her to scream and act strangely. Later, Mr. Stapleton apologizes for her behavior.
Watson and Henry confront the butler. Mrs. Barrymore arrives and explains everything. The escaped swindler is her brother, and they’ve been feeding him. Henry and Watson go to capture the man. On their way, they hear the loud wail of a wolf. They find where the scam is hiding. The man escapes, but Watson sees a different figure, but it quickly disappears. They agree not to tell the police and Barrymore thanks them by giving them another lead on Sir Charles. He that he went to the door the night he died to meet a woman, and speaks of a letter, signed LL
Watson learns that Frankland’s daughter, Laura Lyons, was married against her father’s wishes and was abandoned by both her husband and her father. The shadow, Selden has seen her and tells her that the man lives in a hut and receives his food from a child. Laura admits that she wrote to him about her and that it was Stapleton who told her about her. He asks her what happened that night, but she says that she missed the date and refuses to say why, adding that she got help from someone else.
Watson looks for the stranger and finds the cabin, and there he awaits his return, it is Holmes. He then explains why he lied to Watson. He reveals that Laura and Mr. Stapleton had an affair and that his sister is really his wife. Holmes recounts his search for Stapleton’s past. They hear a scream on the moor. When Stapleton sees that the body is not Henry and acts strangely. A portrait reveals a comparison between Hugo and Stapleton, giving a clear motif. Holmes tells Henry that they are going to London and tells Henry to trust him. They go to tell Laura about Stapleton’s marriage. She reveals that he had offered to marry her if he divorced her, but that he would need Charles’s help. He wrote Laura’s letter to Charles and then insisted that she not go.
The detectives hide and a thick fog settles. They hear the hound and shoot at it, but they don’t die, then it jumps on Henry, but Holmes shoots more and the hound goes down. They find that it is covered in phosphorous to make it glow. They knew that the brilliance of the hound was what scared Sir Charles to death. Finding Mrs. Stapleton bound and gagged, she tells them about her husband’s hiding place and she leads them through the mud. They find in a nearly submerged black boot that belonged to Sir Henry. Stapleton’s tracks are gone and they decide the mud has killed him.
Back in London, Henry and Mortimer visit them to find out all the details of the case. Stapleton was actually the son of Roger Baskerville, and that he went to Devonshire to plan his fate in the Baskerville inheritance. Stapleton took his wife with him to London, where he followed Henry and she tried to warn him. She stole one of Henry’s shoes to give the hound scent on him. Holmes then claims that the letter smelled of perfume and that the idea of a woman made him think of the Stapletons and how she used Henry to trap Stapleton. Mrs. Stapleton warned Henry but did not reveal her husband. When Henry came to dinner, he noticed that he had his bloodhound in the outhouse and confronted him. He told her about her relationship with Laura, she reacted and he tied her up and gagged her. The only thing left unexplained is how Stapleton intended to claim the fortune. Holmes has a guess, but admits that he cannot foresee the future.
