British noblewoman Mary Morstan was surprised when she received a strange invitation letter. So he came to ask Holmes for help. Holmes also felt that there was something strange about the matter, and he and Watson took the initiative to accompany Mary to the appointment. The inviter was a gentleman who called himself Thaddeus Shurdo. Mr. Shurdo's father was Colonel Shurdo, a military colleague of Mary's father, Captain Morstan. The death of Mary's father was actually inseparable from the old Shurdo. relationship, so Thaddeus hopes to compensate Mary. Thaddeus' brother Bartholomew discovered the treasure left by his old father, so Thaddeus decided to give part of the property to Mary. However, when Thaddeus went to his brother Bartholomew's home, he found that Bartholomew dead. Holmes traced clues to a man named Jonathan Small. It turned out that Small was the owner of the treasure. Old Shurdo and Captain Morstan had robbed the treasure, so Small vowed to make a fortune. Qiu retrieved the treasure, which resulted in Tonga's death.