Sherlock Holmes (Basil Rathbone) and Dr. Watson (Nigel Bruce) are on the trail of a plot that threatens to destroy the financial fabric of England. An unscrupulous prison inmate, who stole engraving plates from the Bank of England, has hidden them in a series of music boxes. When the innocent owners of the music boxes start turning up dead, it's up to Holmes and Watson to find the remaining music box, before an unsavory collection of criminals do. The repartee between Rathbone and Bruce is delightful as always.