A Mary Morsten comes to Sherlock Holmes, who asks him and the doctor to help solve the problem of getting her a pearl every year and help in finding her father who disappeared many years ago. Holmes and Watson do not refuse her help and find out that Miss Mary is the heiress of a huge fortune, which is also claimed by the sons of Major Sholto and the convict with a wooden prosthesis instead of the leg, Jonathan Small, whom the older Morsten and Sholto tricked (while Sholto tricked and Morsten) . The savage Tonga - Jonathan Small’s assistant - kills one of Sholto’s sons, and Small steals the treasures, but Holmes attacked the trail and, together with Inspector Lestrade and several police officers, rushes to chase the Thames. During the persecution, the savage is killed, but Jonathan Small manages to gradually throw all the gems into the river. As a result, the treasure that brought so much trouble does not go to anyone. However, during the search, Dr. Watson and Miss Morsten fell in love and decided to get married.