Don Florestan is a personal enemy of the governor Don Pizarro and also a confidant of the minister Don Fernando. As Pizarro sees Florestan as a threat, he wants to eliminate him. He cannot bring himself to commit open murder, so he has him secretly imprisoned and hopes that he will soon die of his own accord. Florestan's wife Leonore suspects that Pizarro is behind her husband's disappearance. Disguised as a man, she sets off in search of Florestan and, under the name "Fidelio", takes up service as an assistant to the jailer Rocco - she suspects Florestan is in the prison he administers and hopes to free him.