This is a classic Sherlock Holmes mystery story. It takes place in the late 19th century, specifically in April 1883. The narrator is Watson, who is the friend and assistant of Sherlock Holmes, a brilliant but somewhat antisocial detective. Holmes’s behavior is bizarre and off-putting. He can be rude and esoteric, and while Watson puts up with his eccentricities, clients are often appalled.
A woman, Helen Stoner, comes to hire them because her twin sister Julia died while staying at the family ancestral house Stoner Manor, where their stepfather Dr. Roylott is living. Her last words were about a speckled band. The house is creepy and mostly unlivable, and Dr. Roylott has a strong temper and has a lot of exotic and dangerous Indian-imported pets.
Holmes and Watson go to stay at the house to solve the mystery, but Dr. Roylott repeatedly tries to intimidate Holmes. One of my favorite parts is when Dr. Roylott bends a poker to show how strong he is, and Holmes is not at all intimidated and bends it back when he leaves, demonstrating that he is just as strong. Holmes notes that there is a bell cord but no bell. The speckled band turns out to be a venomous Indian snake called a Swamp Adder, and the strange whistling Helen heard was Dr. Roylott calling the snake back after it bit Julia, causing her death.