Irene, Sherlock, and Lupin have arranged to meet in London. However, Lupin does not show up. His father is arrested, accused of robbery and the murder of Alfredo Santi, the secretary of the famous composer Giuseppe Barzini. The children begin an investigation to clear Lupin's father of the charges. The rescue of the great soprano Ophelia Meridiu in the notorious district of Bethnal Green is only the beginning of a series of events that will lead Sherlock and his friends to uncover the real culprit.