Rupert of Hentzau, conspirator against the King of Ruritania who is exiled and thought to be dead, secretly returns to Ruritania. On the road he intercepts a letter from the unhappy Queen Flavia summoning her English lover, Rudolph Rassendyll, who was once able, owing to his striking resemblance to the monarch, to impersonate and rescue the king from conspirators who had vowed to kill him. Rupert kills the king and, intending to use the purloined love letter to establish himself on the throne, threatens Rudolph that he will reveal the contents of the letter unless his terms are met. Rudolph and Rupert fight a duel, and Rupert is slain. Rudolph refuses the offer of the throne and returns to England, where Queen Flavia, having abdicated, soon joins him.