Sherlock Holmes, the famous detective known for his powers of observation and deduction.
Dr. John Watson
Dr. John Watson, Holmes’s friend and assistant. In this story, he is attracted to Mary Morstan, proposes to her, and is accepted.
Mary Morstan, Holmes’s client. She is a young Englishwoman whose father, an officer with an Indian regiment, failed to meet her, as he had sent word he would, at a London hotel. Her father has been missing for ten years.
Major Sholto, a friend and brother officer of Miss Morstan’s father. He reveals to his two sons that Morstan died accidentally as they argued over some jewels that had been handed over to them for transportation from India to England. He refuses to relinquish the fabulous jewels and is relentlessly hounded by the Four. He dies strangely before he can reveal their hiding place to his sons.
Dr. Thaddeus Sholto
Dr. Thaddeus Sholto, an art collector, one of the major’s twin sons. Trying to share his wealth with Mary Morstan, he sends her a pearl each year. He learns that his twin brother has located the treasure chest, and he so informs Mary Morstan and Holmes.
Bartholomew Sholto, Dr. Sholto’s twin brother. After having located the jewels in his dead father’s attic, he is found murdered.
Jonathan Small, Holmes’s key to the mystery. When captured, he tells that he is one of the Four, four men who accidentally discovered the jewels in India. Imprisoned after an uprising, they gave the secret of the treasure to Major Sholto and the now dead Morstan. Small and one of the other men sought to regain the treasure, committing murder in doing so. About to be captured, Small dumps the jewels in the river.