In The Adventure of the Speckled Band, Sherlock Holmes and Dr. Watson solve a case involving the murder of a young woman in a room at her stepfather's house. The woman's last words referred to a speckled band. Her sister, Helen, now stays in the same room and fears for her own safety. The stepfather, Dr. Roylott, has many exotic animals in his home, which gives Holmes a clue. Holmes and Watson spend the night in the locked room, a recurring theme in the stories, and figure out the case.
Sherlock Holmes and Dr. Watson rise unusually early one morning to meet a young woman named Helen Stoner. Helen fears that her life is being threatened by her stepfather, Dr Grimesby Roylott, a doctor who practiced in India and was married to Helen’s late mother there years earlier. Dr. Roylott is the impoverished last survivor of what was a wealthy but violent, ill-tempered and amoral Anglo-Saxon aristocratic family of Surrey, and has already served a jail sentence in the past for killing his Indian butler in a rage. Helen’s twin sisterhad died almost two years earlier, shortly before she was to be married. Helen had heard her sister’s dying words, "The speckled band!" but was unable to decode their meaning. Helen, herself is now engaged, and she has begun to hear strange noises and to observe strange activities around Stoke Moran, the impoverished and heavily mortgaged estate where she and her stepfather live.
Dr. Roylott also keeps strange company at the estate - he is best friends with a band of Gypsies on the property, and has a cheetah and a baboon as pets. For some time, he has been making modifications to the home. Before Helen’s sister’s death, he had modifications made inside the house, and is now having the outside wall repaired, forcing Helen to move into the room where her sister died.
Holmes listens carefully to Helen’s story and agrees to take the case. He plans a visit to the manor later in the day. Before he can leave, however, he is visited by Dr Roylott himself, who threatens him should he interfere. Undaunted, Holmes proceeds, first to the courthouse, where he examines Helen’s late mother’s will, andthen to the countryside.
At Stoke Moran, Holmes inspects the premises carefully inside and out. Among the strange features that he discovers are a bed anchored to the floor, a bell cord that does not work, and a ventilator hole between Helen’s temporary room and that of Dr Roylott's.
Holmes and Watson arrange to spend the night in Helen’s room. In darkness they wait; suddenly, a slight metallic noise and a dim light through the ventilator prompt Holmes to action. Quickly lighting a candle, he discovers on the bell cord the "speckled band" - a venomous snake. He strikes the snake with a stick, driving it back through the ventilator agitated, it attacks Roylott, who had been waiting for it to return after killing Helen. Holmes then reveals to Watson the motive: the late wife's will had provided an annual income of 750 GBP of which each daughter could claim one third upon marriage. Thus Dr. Roylott plotted to remove both of his stepdaughters before they married to avoid losing most of the fortune he controlled when the daughters took with them their share of money left for them by their mother from their birth father's estate.