Holmes and Watson return from a vacation at Brighton to find an impostor has been impersonating Holmes, misadvising Lestrade to guard Hambleburg's not Carrolton's jewelry store and Sir Arthur to hide his valuables in the biscuit jar. Fighting impersonation with impersonation, Watson becomes the maharaja of Gampoor.

A chemist is accused of the murder of his fiancé's stepfather, who was determined to keep the two apart. Although there is mounting evidence of the chemist's guilt, Holmes is requested by the old man's housekeeper to investigate the case, as she believes the young man to be innocent.