The Sign of the Four is an 1890 detective novel, and it is the second novel featuring Sherlock Holmes by British writer Sir Arthur Conan Doyle. Doyle wrote four novels and 56 short stories featuring the fictional detective.
In 1888 Miss Mary Morstan arrives 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 once a year for six years. With the sixth pearl, she 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.
