E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A state prisoner of Seville, married to Leonora, who, in mans disguise, and under the name of Fidelio, became the servant of Rocco, the jailor. Pizarro, governor of the prison, conceived a hatred to Fernando, and resolved to murder him. Rocco and Leonora were sent to dig his grave, and when Pizarro entered the dungeon, Leonora intercepted his purpose. At this juncture the minister of State arrived, and ordered the prisoners release. (Beethoven: Fidelio.)