The following are the contents of the libretto:
Robert, Duke of Normandy, has a friend of gloomy exterior, named Bertram, with whom he travels, but to whose evil influence he owes much trouble and sorrow. Without knowing it himself, Robert is the son of this erring knight, who is an inhabitant of hell. During his wanderings on earth he seduced Bertha, daughter of the Duke of Normandy, whose offspring Robert is. This youth is very wild and has therefore been banished from his country.
Arriving in Sicily, Isabella the King's daughter and he fall mutually in love.
In the first act we find Robert in Palermo, surrounded by other knights, to whom a young countryman of his, Raimbaut, tells the story of "Robert le Diable" and his fiendish father; warning everybody against them. Robert, giving his name, is about to deliver the unhappy Raimbaut to the hangman, when the peasant is saved by his bride Alice, Robert's foster-sister. She has come to Palermo by order of Robert's deceased mother, who sends her last will to her son, in case he should change his bad habits and prove himself worthy. Robert, feeling that he is not likely to do this, begs Alice to keep it for him. He confides in the innocent maiden, and she promises to reason with Isabella, whom Robert has irritated by his jealousy, and who has banished him from her presence.
As a recompense for her service Alice asks Robert's permission to marry Raimbaut. Seeing Robert's friend, Bertram, she recognizes the latter's likeness to Satan, whom she saw in a picture, and instinctively shrinks from him. When she leaves her master, Bertram induces his friend to try his fortune with the dice and he loses all.
In the second act we are introduced into the palace of Isabella, who laments Robert's inconstancy. Alice enters bringing Robert's letter and the latter instantly follows to crave his mistress' pardon. She presents him with a new suit of armor, and he consents to meet the Prince of Granada in mortal combat. But Bertram lures him away by deceiving him with a phantom. Robert vainly seeks the Prince in the forest, and the Prince of Granada is in his absence victorious in the tournament and obtains Isabella's hand.
The third act opens with a view of the rocks of St. Irene, where Alice hopes to be united with Raimbaut. The peasant expects his bride, but meets Bertram instead, who makes him forget Alice, by giving him gold and dangerous advice. Raimbaut goes away to spend the money, while Bertram descends to the evil spirits in the deep. When Alice comes, Raimbaut is gone, and she hears the demons calling for Bertram. Bertram extracts a promise from her not to betray the dreadful secret of the cavern. She clings to the Saviour's cross for protection, and is about to be destroyed by Bertram, when Robert approaches, to whom she decides to reveal all. But Bertram's renewed threats at last oblige her to leave them.
Bertram now profits by Robert's rage and despair at the loss of his bride, his wealth and his honor, to draw him on to entire destruction. He tells Robert that his rival used magic arts, and suggests that he should try the same expedient. Then he leads him to a ruined cloister, where he resuscitates the guilty nuns. They try to seduce Robert first by drink, then by gambling, and last of all by love. In the last, Helena, the most beautiful of the nuns, succeeds and makes him remove the cypress-branch, a talisman, by which in the fourth act he enters Isabella's apartment unseen. He awakes his bride out of her magic sleep, to carry her off, but overcome by her tears and her appeal to his honor, he breaks the talisman, and is seized by the now awakened soldiers; but Bertram appears, and takes him under his protection.
The fifth act opens with a chorus sung by monks, which is followed by a prayer for mercy. Robert, concealed in the vestibule of the cathedral, hears it full of contrition. But Bertram is with him, and, his term on earth being short, he confides to Robert the secret of his birth and appeals to him as his father.
He almost succeeds, when Alice comes up, bringing the news that the Prince of Granada renounces Isabella's hand, being unable to pass the threshold of the church. Bertram urges Robert all the more vehemently to become one with him, suggesting that Isabella is likewise lost to him, who has transgressed the laws of the church, when in the last extremity Alice produces his mother's will, in which she warns him against Bertram, entreating him to save his soul. Then at last his good angel is victorious, his demon-father vanishes into the earth and Robert, united by prayer to the others, is restored to a life of peace and goodness.