The third part of the Soviet TV series based on the works of Arthur Conan Doyle about Sherlock Holmes. The events of the film take place in 1889. The country doctor Mortimer comes to Sherlock Holmes and Dr. Watson, who visited the detective's apartment the day before in his absence and forgot his cane there. Mortimer tells the legend of the Hound of the Baskervilles, a hellish hound that has been haunting the Baskerville family from Devonshire for several centuries, and reports the mysterious death of Sir Charles Baskerville, the owner of the Baskerville Hall estate. The newspapers write that Charles Baskerville's death was caused by a heart attack, allegedly he was very unwell, but Mortimer does not believe a single word of them, since he found tracks of a huge dog not far from the body of the deceased.