The novel is narrated by Dr John Watson who accompanies the main character, Sherlock Holmes, a private detective. The novel begins with Holmes complaining of boredom. Miss Mary Morstan arrives at Baker Street with a mystery regarding her missing father and an annual anonymous gift of pearls she has received for several years.
Holmes is glad to take on the case, as it will occupy his mind. Watson is also happy because he finds Miss Morstan attractive. They are taken to Thaddeus Sholto who explains how his father and Captain Morstan died. His brother, Bartholomew, is found dead in his home and then Holmes uses the clues to unravel the mystery of his murder and the hidden treasure. He rightly deduces that both Jonathan Small and his accomplice are involved.
At the end of the novel, having solved the case, we see Holmes return to his state of boredom.