In turn-of-the-century England, Dr. Mortimer visits well-known detective Sherlock Holmes and his friend Dr. Watson to relate the story of the curse of the Baskervilles: In the late 18th century, Sir Hugo Baskerville, reputed for his cruelty and arrogance, tracks a local farm girl to the nearby abbey ruins where he assaults her and stabs her to death only to be attacked and killed by a mysterious, huge dog moments later. In the present, Mortimer explains that Sir Charles Baskerville has just died a few days earlier, his body found in the same abbey ruins where Hugo met his demise. Upon learning specific details of the death, Holmes concludes that Charles died of fright, but agrees to meet his nephew, Sir Henry, the last of the Baskervilles, who is arriving from South Africa to take over Baskerville Hall in Dartmoor. The following day, Holmes and Watson meet Mortimer and Henry at a hotel where Henry dismisses Mortimer's fear of a curse on the family and reveals that he will be inheriting a million pounds from Charles's death. Holmes declares that he is unable to accompany Henry to Dartmoor, but asks Watson to provide an escort. Still skeptical, Henry complains about his missing boot, only to be terrified when a large tarantula crawls out of his remaining boot and up his arm before Holmes hits it away and kills it. Holmes suggests that the spider was placed there intentionally and advises Henry to be cautious. Mortimer and Watson accompany Henry on his journey to Baskerville Hall and when Mortimer departs to walk into the village, Perkins, the coach driver, warns him that a dangerous convict, Seldon, has escaped from a nearby prison and is reported to be hiding on the moors. At Baskerville Hall, Henry and Watson meet Mr. and Mrs. Barrymore, the hall's butler and cook. That night, Watson is awakened by the sound of a woman weeping from a room at the top of the house and is startled when he clearly hears a distant howl of a dog. The next morning, Henry is welcomed to the area by kindly but bumbling Bishop Franklin who also informs Henry of the coming village "jumble" sale over which he must preside. Meanwhile, Watson walks into the village and on his return nearly steps into a hunting trap, but is warned in time by a farmer, Stapleton. In explaining his use of traps instead of a gun, Stapleton shows Watson his webbed and crippled hand, then alerts him to the dangerous mires in the area. A little later, Watson comes across a young woman sitting on a boulder. Refusing to answer the doctor's query, the girl flees and when Watson follows, he falls into a bog, where he is rescued by Stapleton. The girl, Stapleton's daughter Cecile, joins the men on the cart ride back to the hall and she apologizes to Watson, claiming she thought he might be the escaped convict. At the hall, Henry is captivated by Cecile's rough charm. That night, Henry is awakened by the sound of a woman weeping and, together with Watson, examines the spare room, which they find empty. Watson then spots a light across the moor and the men race outside after it. As they find a solitary lantern on a hill near the ruins, Henry is startled by the appearance of a strange figure and collapses. Although Watson sees a caped figure standing in the ruins, he ignores it to help Henry back to the hall. Before returning to the ruins, Watson summons Mortimer and makes him promise to remain with Henry. Hurrying back to the abbey, Watson is surprised to find that the caped man is Holmes, who explains that he has been there investigating privately since the day they arrived. Holmes admits the strange figure was indeed the escapee, Seldon, with whom he spoke at length. The men's discussion is interrupted by the distant howling of a dog. Hurrying to the top of the hill, Holmes notes that Mortimer's cart is no longer at the hall and as they hasten out across the moor, they hear a man screaming. Following the sound, the men find a mauled body whose tweed clothes match those of Henry. Returning to the hall, Holmes is taken aback to find Henry alive and deduces that Seldon was the victim of the attack. The next morning, Holmes, Barrymore and Watson return to the moor, but are unable to find Seldon's body until they are led by bloodstains to the abbey, where they find the horribly mutilated body and a large knife. Later, Holmes interviews the Barrymores and tricks Mrs. Barrymore into admitting she is Seldon's sister. Mrs. Barrymore acknowledges giving Seldon clothes that Henry had donated for the jumble sale, and hanging a lantern near the abbey as a signal when it was safe to bring Seldon food. Holmes then calls upon the bishop, who he has learned is an expert entomologist and collector of spiders, and discovers his recent loss of a rare tarantula just after being visited by Mortimer and a man named Smith. Interested in seeing Cecile again, Henry visits her at her farm where she describes the great difficulties she and her father have had running the farm. Henry asks her to meet him that evening on the moor and she agrees. Meanwhile, Holmes tells Watson that Seldon mentioned hearing the howling of a dog from underneath the ground. Examining a map, Holmes learns of an abandoned silver mine located under the Stapleton property and, accompanied by Stapleton, Perkins and Mortimer, visits the mine. While Holmes is deep inside the mine, a runaway hand cart breaks loose and crashes into several beams, causing a cave-in. The others dig furiously but are unable to get back into the mine. Moments later, however, they find Holmes waiting for them at the cart, having escaped through one of the mine's many tunnels. At the hall, Holmes shows Watson a large bone he discovered in the mines, then grows anxious upon discovering that the knife from the ruins has been stolen from his room. Henry informs Holmes and Watson of a dinner invitation from the Stapletons, but Holmes refuses, sending Henry off alone, to Watson's bewilderment. When Watson asks Holmes about a missing portrait of Hugo that hung in the stairway, the detective reveals that Barrymore told him that the portrait revealed that Hugo had a webbed and deformed hand, like Stapleton, confirming Holmes's suspicion that Stapleton is a Baskerville descendent responsible for the mysterious deaths in an attempt to gain the Baskerville inheritance. Explaining that Henry is being lured into a trap that evening, Holmes takes Watson to the moor where Henry has met Cecile. To Henry's surprise, Cecile rejects his amorous advances and reveals that she and her father are also Baskervilles who have been denied their rightful inheritance. At that moment there is a howl and a huge dog leaps from the ruins onto Henry, who manages to knock the creature out. Stapleton then appears and threatens Henry with the knife, but is shot by Watson, who has arrived with Holmes. Watson shoots the reviving dog as Cecile struggles for the knife, but Holmes intervenes, sending the girl racing across the moor and into the mire. Holmes then tells the shaken Henry that in the mine he discovered a passageway to the abbey ruins and found a bone and Henry's lost boot, provided to incite the starved dog, who was held by the Stapletons until needed for an attack. With the "curse" officially lifted from the Baskervilles, Holmes and Watson return to London.
