Answer: Miss Mary Morstan comes to Holmes with the mystery of her missing father, the yearly pearls and a strange letter.
Miss Morstan’s father, Captain Arthur Morstan, an officer of an Indian regiment, returned to London in 1878 and disappeared from his hotel on the very day he arrived; he was never found. About four years later, after an advertisement in a newspaper asked for her address, she began to receive a large, lustrous pearl by post every year from an unknown sender — six in all. That morning she received a letter asking her to come to the third pillar outside the Lyceum Theatre that evening, bringing two friends but no police, as she was a wronged woman. She asks Holmes to accompany her.