Title and Credits are shown over a painting of Baskerville Hall on a hill top during a storm. A narrator tells us, "Know then the legend of the Hound of the Baskervilles. Sir Hugo a wild, profane and godless man; An evil man, in truth for there was with him a certain ugly and cruel humor that made his name a byword in the county." A drunken party is underway and a servant is tortured by Sir Hugo (David Oxley). The servant's daughter is the prize, but she has left the house. Furious, Sir Hugo sets the hounds on her trail, "The hounds: Let loose the pack!" The servant girl escapes on the estate, Sir Hugo gives chase and both hear the loud baying of a hound. The girl takes refuge in the old abbey ruins, but Sir Hugo finds her. In a fit of rage, he stabs her with a dagger. He hears the hound. It attacks and kills him."And so, the curse of Sir Hugo came upon the Baskervilles in the shape of a hound from Hell, forever to bring misfortune to the Baskerville family. Therefore, take heed and beware the moor in those dark hours when evil is exalted else you will surely meet the hound of Hell, the hound of the Baskervilles." Dr. Mortimer (Francis De Wolff) reads this last passage to Sherlock Holmes (Peter Cushing) at his Baker street residence. Holmes is unimpressed and Dr. Mortimer is perturbed. Holmes asks the real reason for his visit. "The body of Sir Charles Baskerville discovered on Dartmoor early today," Dr. Mortimer reads from a local newspaper. Sir Charles was found by a servant, Barrymore, near the abbey ruins up on a hill not far from Baskerville Hall. The coroner's inquest ruled it heart failure. Dr. Mortimer's desire is to have Holmes investigate the matter because he thinks Sir Henry is in danger. Holmes agrees to see Sir Henry at his hotel the next day. Dr. Watson (Andre Morell) sees Dr. Mortimer out.Sir Henry Baskerville (Christopher Lee) is dressing in his hotel room. Holmes and Watson arrive, but Sir Henry mistakes them for hotel employees that have come to investigate a missing boot. Dr. Mortimer arrives amid the confusion and makes introductions. Sir Henry makes it clear he intends to occupy Baskerville Hall. Dr. Mortimer reluctantly tells Holmes the estate is worth about one million pounds. The will details bequests, including one thousand pounds for the Barrymores, and Dr. Mortimer is to receive forty thousand pounds. Holmes tells Sir Henry that, "I must impress upon you that I believe your life to be in considerable danger." Holmes also tells him that he is unable to leave London at the moment, but he will be sending Dr. Watson along to Dartmoor. Before anyone leaves, the first attempt on Sir Henry happens. A poisonous tarantula is hidden in a boot and crawls up near Sir Henry's head, but Holmes dispatches it.Sir Henry, Watson and Dr. Mortimer arrive in Dartmoor. Dr. Mortimer exits the cart for a short walk home. Before he walks away Perkins, the cart driver (Sam Kydd) suggests that Dr. Mortimer not walk alone. He tells him there has been a prison escape and a man named Selden, sentenced to life imprisonment is out on the moors. Sir Henry and Watson proceed to Baskerville Hall while Dr. Mortimer walks home. They are met at the Hall by Barrymore (John Le Mesurier). He gives the new master a tour of the house, and shows him a portrait of Sir Hugo. He tells him of the legend. Sir Henry notices a missing portrait, another of Sir Hugo. He is told it disappeared a few months ago. Watson is at the table finishing his meal. Sir Henry offers a toast, but Mrs. Barrymore (Helen Goss), visibly upset drops her glass then excuses herself. Dr. Watson asks Barrymore about the death of Sir Charles, as he found the body. Dr. Watson asks Barrymore if he believes in the legend of the hound. Barrymore tells Dr. Watson that he has heard the terrible howl.Dr. Watson is awakened in the night to the sound of a woman moaning. He investigates but finds nothing. The next morning the local Vicar, Bishop Frankland (Miles Malleson) stops to ask Sir Henry for a donation to the church. He is invited in for a glass of sherry. Sir Henry asks Mrs. Barrymore to donate an old suit to the jumble sale. Dr. Watson stops at the Grimpen Post Office to get a telegram from Holmes. It reminds Watson, "Under no circumstances allow Sir Henry to venture on the moor alone at night." Dr. Watson walks back to Baskerville Hall through the moor. He encounters Stapleton (Ewen Solon) who warns the doctor he was about to step into a trap. Stapleton also warns Watson to stick to the trail, lest he fall into the Grimpen Mire. Along the walk he encounters Cecile Stapleton (Maria Landi). Watson asks her if he is on the right path to Baskerville Hall. She bolts without answering, and Watson follows her but he falls into the mire. Stapleton rescues him, Cecile returns and helps. The Stapletons, father and daughter, return Dr. Watson to Baskerville Hall. Watson and Stapleton go into the house, and Cecile remains in the cart outside. They don't know Sir Henry is out riding his horse. Sir Henry arrives and talks to Cecile. She is very rude to Sir Henry. She runs away and when confronted, she kisses Sir Henry.That evening after everyone else has gone to bed, Sir Henry is joined by Dr. Watson. They see a light under the door of an unoccupied room. A candle burns near a window. Sir Henry notices a light out on the moor--a signal. Dr. Watson and Sir Henry investigate outside and find the source of the light. They find Selden (Michael Mulcaster), the escaped convict. They give chase and hear the hound. Sir Henry suffers a mild heart attack. Dr. Watson helps him back to the hall. Dr. Mortimer examines Sir Henry and orders bed rest. Dr. Watson wants Mortimer to stay and watch Sir Henry while he returns to the moor. Watson goes to the abbey ruins and encounters Holmes asking, "Why have you left Sir Henry alone?" Holmes tells Watson he has been in Devon for the whole time gathering information from Selden. "Selden told me all he had seen since hes been hiding." They hear the hound in the distance and run to investigate. Holmes notices Dr. Mortimer left Baskerville Hall. They hear a man scream and rush to investigate. They spot a man they believe to be Sir Henry dead. Holmes and Watson return to Baskerville Hall to get help to move the body. They see a light under the door of the signal room. Inside the room is Sir Henry reading a book. Sir Henry asks, "Who was it Holmes? Who was the poor devil that died instead of me?" Holmes deduces it was Selden, "Selden had on the suit you were wearing when we met in London."The next morning, Holmes and Watson return to the site of the death of Selden. They go to the abbey ruins and there they find blood on a stone and a dagger. Barrymore finds Selden's body, which had been moved from the night before. His body has been mutilated. "Some revolting sacrificial rite has been performed," Holmes notes. At the Hall, Holmes confronts Mrs. Barrymore and extracts the confession she was aiding her brother, Selden. She gave him food and Sir Henry's clothes and used the candle as a signal.Holmes pays a visit on the Bishop to inquire about a missing spider. Holmes knows the Bishop is regarded as the highest living authority on the study of rare spiders. He asks about the genus Theraphosa--tarantula. Bishop Frankland finally admits he is missing a tarantula and volunteers his visitor list, which included Dr. Mortimer and the Stapletons.Sir Henry stops at the Stapleton cottage. He lets himself in when no one answers his knock. Cecile appears and asks, "Why did you come here?" Stapleton is out and Cecile tells Sir Henry he is invited for dinner. She tells Sir Henry she is Spanish and her mother is dead. Her father returned to farm, but the property is no good. Sir Henry is in love with Cecile. Stapleton walks in and sees his daughter and Sir Henry being intimate. They sit and have a drink.Holmes and Watson meet with and confront Dr. Mortimer. They suspect he may have had a hand in the strange circumstances surrounding the death of Sir Charles and the attempts on Sir Henry. They ask about an old tin mine on the property. Mortimer tells Holmes that Stapleton may be more help as it is under his land. Holmes insists in seeing the mine, and insists that Dr. Mortimer accompany him. Holmes shows Mortimer the dagger that was used on Selden and the same as Sir Hugo used to kill the servant girl centuries earlier.Stapleton, Dr. Mortimer, and Holmes explore the old tin mine. Watson stays above. It is dank and water seeps through from the mire above. Holmes is looking for bones. While Stapleton and Mortimer chock the wheels of an old mining cart, Holmes explores deeper. He tells the two men, "We won't need to go any further, I've found what I came down for." They hear the hound howling. The cart runs down the rails, hits a support beam and causes a cave in, trapping Holmes. They dig for a while, but after two hours they stop. As it turns out, Holmes is waiting in the cart. He hurt his leg. Back at Baskerville Hall, Sir Henry invites Holmes and Watson to join him for dinner at the Stapletons. Holmes is very rude to Sir Henry. This is his plan--he wants Sir Henry to leave without them. The dagger is missing and Holmes has learned that Sir Hugo's hands were webbed, like Stapleton's hands. It turns out Stapleton is next in line for the Baskerville fortune. Holmes and Watson head for the abbey ruins where Sir Henry and Cecile have gone. She is leading Sir Henry to her father, the hound, and certain death. Fortunately Holmes and Watson hear Cecile's plan as she tells Sir Henry he will die. The hound appears and leaps on Sir Henry. It begins to maul him. Stapleton attacks Watson as he tries to shoot the hound. They scuffle briefly but Watson manages to shoot Stapleton. Holmes shoots the hound which turns on Stapleton. Cecile retrieves the dagger and tries to finish Sir Henry off, but Holmes intervenes. Cecile escapes. Holmes and Watson help Sir Henry to his feet and show him the dead dog. The dog was kept in the mine, starved for weeks, given the scent and turned loose. His missing boot was the scent. Cecile still running slips into the mire and is pulled under.Back in London Holmes and Watson admire a gift sent by Sir Henry. It is the missing portrait of Sir Hugo, showing his deformed hand, as a souvenir Holmes can add to his collection. Sir Henry also included a check for a very generous amount. Watson asks Holmes about what clue was the key. Holmes quips that, "the missing boot put me on the scent." We close with Holmes and Watson having tea.