A young lady calls on the narrator's colleague because he had helped Mrs. Cecil Forrester; she describes the disappearance of her father, a series of pearls she has received yearly on May 4th, and a mysterious letter asking Miss Morstan to meet an "unknown friend" outside the Lyceum Theatre.  
At one point in this story, a character recommends Winwood Reade's Martyrdom of Man. The narrator compares his colleague's misplaced romanticism to working a love-story into Euclid's Fifth Postulate. A young lady calls on the narrator's colleague because he had helped Mrs. Cecil Forrester; she describes the disappearance of her father, a series of pearls she has received yearly on May 4th, and a mysterious letter asking Miss Morstan to meet an "unknown friend" outside the Lyceum Theatre.  When that character returns, she brings a piece of paper from her father's desk with the names Mahomet Singh, Abdullah Khan, Dost Akbar and Jonathan Small written on it. Preceded by A Study in Scarlet, for 10 points identify this novel about Sherlock Holmes by Sir Arthur Conan Doyle named for a hieroglyphic symbol.
At one point in this story, a character recommends Winwood Reade's Martyrdom of Man.
The {Sign} of the {Four}