The Sign of the Four by Sir Arthur Conan Doyle [Sherlock Holmes #2]

In THE SIGN OF THE FOUR (the second Sherlock Holmes mystery), a distressed and beautiful young lady arrives at the offices of Sherlock Holmes. Each year following the strange disappearance of her father, Miss Morstan has received a rare and lustrous pearl. Now, on the day she is summoned to meet her anonymous benefactor, she comes to consult with Holmes and Watson.