By chance, two middle-aged people met - the telephone operator of the hotel Lina and the chief engineer of the construction department Kirillov, who had arrived on official business from Leningrad in one of the provincial cities of the country. Behind everyone has setbacks in family life. A sincere feeling that brought two lonely people closer together helped to see those around them in a new way. They are already over forty. Both are lonely. Having met by chance and fell in love with each other, they never became happy.

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).