It is spring in Baker Street, and London is preparing itself for the wedding of the season - an international spectacular in which the young and popular Duke of Krasnow, a political exile from his native land, is due to take the hand of the beautiful and accomplished Princess of Rovenia - a union that will heal the divisions between her family and the duke's. But the stakes are high.

When the princess subsequently disappears in dramatic circumstances, other members of the British establishment are quick to call on Mr Sherlock Holmes and he, in turn, looks to longstanding housekeeper Mrs Hudson, and her able assistant housemaid Flotsam, to assist in this puzzling case.