In 1888 Miss
Mary Morstan arrives at the flat of Sherlock Holmes with a case. She explains that, ten years earlier, her father Captain Arthur Morstan disappeared immediately after arriving in London from his military service abroad. Mary contacted his friend, Major Sholto, who denied having seen him. Four years later she received a valuable pearl in the post, a gift repeated every year for six years. With the sixth pearl, she also received a letter asking for a meeting, claiming that she is a "wronged woman". Holmes takes the case and soon discovers that Major Sholto had died a week before Mary received the first pearl. The only further clue Mary can give Holmes is a map of a fortress found in her father's desk, appended with the words, "The Sign of the Four: Jonathan Small, Mahomet Singh, Abdullah Khan, Dost Akbar" and four small cross-like symbols. Following the letter's instructions, Holmes, Watson and Mary go to the
Lyceum Theatre, where they meet a coachman who takes them to the house of Major Sholto's son, Thaddeus, the anonymous sender of the pearls. He reveals that Captain Morstan did, in fact, visit Major Sholto, demanding his half of a treasure that Sholto had secretly brought back from
India. In the ensuing quarrel, Captain Morstan suffered a heart attack and died, striking his head on the treasure box as he fell. Afraid he would be suspected of murder, Major Sholto buried the body and hid the treasure, leaving out a small gold
chaplet studded with twelve pearls. Thaddeus and his twin brother Bartholomew only learned of this when their father revealed it while on his deathbed; he was about to reveal to them where the treasure was hidden, when a bearded man appeared at the window and the Major died of fear. The brothers tried and failed to catch the intruder and later on, found a note pinned to the Major's body which read "The Sign of Four". Thaddeus began sending Mary the pearls to make things right and the brothers searched for the treasure. Six years later, Bartholomew found and withheld it; Thaddeus then contacted Mary so they could both confront Bartholomew and demand their shares. The party, now accompanied by Thaddeus, heads to Bartholomew's house, Pondicherry Lodge,
Upper Norwood. As they enter, the worried housekeeper reveals that Bartholomew has locked himself in his laboratory and refuses to come out. Mary Morstan stays downstairs to comfort the housekeeper, while the others rush up to the laboratory; through the keyhole, they can see Bartholomew slumped in his chair, with a "fixed and unnatural grin" upon his face. Holmes and Watson break down the door, to discover Bartholomew in a state of
rigor mortis. Upon further inspection of the body, Holmes discovers a poisonous thorn above Bartholomew's ear. The treasure box is also gone, though there is a hole in the ceiling where it used to be. While the police wrongly take Thaddeus in as a suspect, Holmes deduces from footmarks and other clues that there are two persons involved in the murder: a one-legged white man named Jonathan Small, and a small
Andamanese accomplice, who accidentally stepped in
creosote. Borrowing a trained scent hound from a naturalist, Holmes traces the pair to a boat landing. Learning that Small has hired a steam
launch named the
Aurora, Holmes, with the help of the
Baker Street Irregulars and his own disguises, traces the boat to a
repair yard. In a police launch, Holmes and Watson pursue the
Aurora when it flees the yard; the islander attempts to shoot a dart at Holmes, but is shot dead himself. Small attempts to flee, running the
Aurora aground, but is captured. However, the treasure box is now empty; Small, not wanting to surrender the gems, had scattered them into the
Thames during the chase. Small confesses that he was once a soldier of the Third
Buffs in India, and lost his right leg to a
crocodile while bathing in the
Ganges. He then became an overseer on an
indigo plantation, but when the
1857 rebellion occurred, was forced to flee to the
Agra fortress. While standing guard one night, he was overpowered by
Sikh troopers, who gave him a choice; be killed, or help them
waylay Achmet, a disguised servant of an outlawed
rajah, who had sent Achmet with a box of jewellery to the British for safekeeping. The robbery and murder took place, but the crime was discovered, although the hidden jewels were not. Small and his accomplices got penal servitude on the Andaman Islands. Some years later, Small learned that Major Sholto and Captain Morstan, who were guards at the convict barracks, had lost money playing cards. Small made a deal with the officers, that Sholto would recover the treasure and in return send a boat to pick up Morstan, Small and the Sikhs so they could all meet and divide it. However, Sholto stole the treasure for himself, returning to England after inheriting a fortune from his uncle. Morstan went after Sholto but never returned and Small vowed vengeance against Sholto. Four years later, Small escaped prison with the help of Tonga, an islander whose life he had once saved. It was the news of this escape that shocked Sholto into his fatal illness. Small arrived too late to hear of the treasure's location, but left the note in the room anyway as revenge for the treatment of himself and the Sikhs. When Bartholomew eventually found the treasure, Small only planned to steal it; however, a miscommunication led Tonga to kill Bartholomew before Small could stop him. Small decides the treasure brings nothing but bad luck to anyone who has it (death to Achmet and Bartholomew, fear and guilt to Major Sholto, imprisonment to Small himself). Mary is left with no treasure, except the pearls, however, she and Watson have fallen in love over the course of the adventure. The loss of the treasure has removed any
barriers there might have been between them and Watson reveals that he has proposed to Mary and she has accepted, much to the annoyance of Holmes. ==Publication history ==