La marque des quatre by Arthur Conan Doyle is a detective novel written in the late 19th century. It follows Sherlock Holmes and Dr. Watson as they investigate Miss Mary Morstan’s troubling case involving her missing father, mysterious pearls sent annually, and whispers of a hidden treasure tied to soldiers from India. The opening of the novel presents Holmes’s restless intellect and cocaine use, his method of observation and deduction (demonstrated through a revealing analysis of Watson’s watch), and the arrival of Miss Morstan with her story: her father vanished years earlier, she has since received yearly rare pearls, and a new letter invites her to a secret meeting. Holmes and Watson accompany her to the rendezvous, are whisked through foggy London to Thaddeus Sholto, who recounts how his father, Major Sholto, concealed Captain Morstan’s sudden death during a quarrel about a trove from India, hid the treasure, feared a one‑legged man, and died amid a mysterious intrusion marked “The Sign of Four.” Thaddeus explains that his twin, Bartholomew, has just found the treasure in a concealed garret, and the group rushes to Pondicherry Lodge, where a wary gatekeeper and a distraught housekeeper deepen the unease. At the top of the house they find Bartholomew’s laboratory locked; through the keyhole they glimpse his ghastly, frozen face, and as Holmes and Watson break down the door, the scene of the first crisis comes into view. (This is an automatically generated summary.)