"The Prisoner of Zenda" (1894), by Anthony Hope, is an adventure novel in which the King of Ruritania is drugged on the eve of his coronation and thus is unable to attend the ceremony. Political forces within the realm are such that, in order for the king to retain the crown, his coronation must proceed. Fortuitously, an English gentleman on holiday in Ruritania who resembles the monarch is persuaded to act as his political decoy in an effort to save the unstable political situation of the interregnum. (Excerpt from Wikipedia)
