Holmes and Dr. Watson help a young lady who is receiving anonymous letters 10 years after her father passed away under shady circumstances. They find themselves in an enigma involving a treasure, murder and a love interest for Watson.

The character of “Die Fledermaus”, Count Eisenstein, is quietly aging on his family estate. Every year he celebrates the birthday of Johann Strauss with great pomp. This time a luxurious ball will be given in honor of the great composer. Rumors are spreading that the great maestro himself will appear here, but incognito.

A girl named Mary Morsten comes to Sherlock Holmes, who asks him and the doctor to help solve the annual receipt of one pearl by her parcel and in the search for 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 — 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 Morsten and Sholto deceived (while Sholto also deceived Morsten).