Dr. Richard Mortimer [Francis de Wolff] recounts to Sherlock Holmes [Peter Cushing] and Doctor Watson [André Morell] in Baker Street the chilling legend of a Hell Hound that is said to have slain the brutal Sir Hugo Baskerville [David Oxley] for the murder of a servant girl’s daughter. He begs Holmes to investigate the death of his dear friend Sir Charles Baskerville on the moor surrounding Baskerville Hall, a landscape steeped in fear and superstition, with Mortimer’s face betraying a deep sense of dread. He warns that Sir Henry Baskerville, the heir who has just arrived from South Africa to claim the vast Baskerville estate—valued at around £1,000,000—might be in imminent danger.
Although Holmes remains skeptical at first, he and Watson agree to meet Sir Henry Baskerville, who explains that one of his boots has gone missing, a clue that seems trivial yet unsettling in a case this ominous. Mortimer’s tale spirals into the strange: a threatening tarantula and an unseen menace that convinces Holmes that danger walks with the Baskervilles. Holmes, claiming that he cannot travel to Baskerville Hall himself, dispatches Watson to Dartmoor with Mortimer and Sir Henry, and firmly admonishes Sir Henry not to set foot on the moor after dark.
On the way to Baskerville Hall, the travelers learn that Selden, a convicted murderer, has escaped Dartmoor Prison and now stalks the moor’s desolate expanse. Upon arrival, Mr. Barrymore [John Le Mesurier] and Mrs. Barrymore [John Le Mesurier] give them the tour of the vast, brooding manor, noting with quiet worry that one of two portraits of Sir Hugo is missing, a discrepancy the couple say has persisted for months.
The following day, Sir Henry meets Bishop Frankland [Miles Malleson], a pastor who also studies insects and knows the land’s lore intimately. Watson, meanwhile, becomes trapped in the Grimpen Mire but is rescued by a local farmer, Stapleton [Ewen Solon], and his daughter Cecile Stapleton [Marla Landi], a young woman who quickly captivates Sir Henry.
That night, a mysterious light on the moor draws Watson and Sir Henry into a tense late-night vigil. They glimpse a shadowy intruder who disappears into the darkness as a distant hound’s cry rips through the air, provoking a mild tremor in Sir Henry’s heart. Watson spots a figure on a distant hill, only to realize the figure is Holmes himself, having traveled in secret to pursue the case more freely.
Selden, wearing Sir Henry’s clothes, is found slain by the unseen hound, his body mutilated in a ritual-like scene near the relic of Sir Hugo’s curved dagger. The Barrymores confess that they aided Selden by supplying food and clothing whenever he signaled with a light from his hideout. Holmes remains convinced that neither the Barrymores nor Selden holds the key to Sir Charles Baskerville’s death, and he reasons that a tarantula in London was stolen from Bishop Frankland.
After surviving danger in an abandoned tin mine in search of evidence, Holmes pieces together the truth: Stapleton and Cecile are both descendants of Sir Hugo, scheming to claim the inheritance by removing Sir Henry from the equation. The nocturnal hound reappears on the moor and attacks Sir Henry, but Holmes shoots the creature, forcing it to retreat. When the dagger of Sir Hugo resurfaces, Stapleton attempts a lethal strike on Watson, only to be wounded by a shot from Watson himself. The wounded hound then turns on Stapleton and mauls him fatally, and Holmes shoots and kills the animal, exposing it as a masked hound rather than a supernatural omen.
Cecile makes one last, desperate bid to escape across the moor, but she sinks into the Grimpen Mire and perishes, leaving Holmes and Watson to shepherd Sir Henry back to Baskerville Hall in astonished silence. Back in Baker Street, Sir Henry returns the stolen portrait of Sir Hugo that had been recovered from the Stapleton farm, a tangible piece of the puzzle finally in place.
