A girl named Mary Morstan comes to Sherlock Holmes and asks him and the doctor to help her solve the mystery of how she receives one pearl every year in a parcel and to find her father, who disappeared many years ago. Holmes and Watson do not refuse to help her and find out that Miss Mary is the heiress to a huge fortune - the treasures of Agra, which are also claimed by the sons of Major Sholto and Jonathan Small - an escaped convict with a wooden prosthesis instead of a leg, whom the elder Morstan and Sholto deceived...

During the investigation of the Agra treasure case, Holmes and Watson recall another case that Holmes had investigated earlier. The King of Bohemia comes to Holmes under a false name, who at first behaves somewhat arrogantly, and then plaintively asks for help. At one time, the king, then still the crown prince, had an affair with the famous adventurer Irene Adler, took a photo with her and signed the photo as a keepsake. Now he is going to get married and wants to avoid a scandal...