Front hall at Ravenswood Castle. In 16th-century Scotland, torn by political strife, the movement to which the Ashtons belong is about to succumb to that of the Ravenswoods. Normanno, head of the armigers in the service of the Ashtons, orders his men to mount an investigation. He in fact suspects that a secret attachment exists between Lucia, Lord Enrico Ashton´s sister, and Edgardo of Ravenswood, the last surviving member of the enemy family. Enrico, who is worried about the Ashtons’ fortunes, confides to Normanno that to save the situation he would like to get Lucia married to Lord Arturo Bucklaw. But he fears his sister’s refusal. Raimondo, Lucia’s tutor and confidant, reminds Enrico that the girl is grief-stricken by the recent death of her mother. But Normanno reveals that the real reason for her sadness is her love of a young man, who saved her life one day when she was charged by a fierce bull. He suspects that the young man in question is none other than Edgardo of Ravenswood. Enrico flies into a rage, and vows to avenge himself. 

In a park, near the siren’s fountain, at dusk, Lucia is deeply upset and confides to her companion Alisa. While waiting for Edgardo, she tells Alisa that she has seen the ghost of a lady, who was murdered for reasons of jealousy by an ancestor of Edgardo’s and cast into the fountain. Alisa urges Lucia to break off her bond, but the girl resolutely refuses. Edgardo appears, and tells Lucia that he will be sailing for France at dawn. Before leaving Scotland however, he wishes to be reconciled with the Ashtons and intends, in token of peace, to request Lucia’s hand in marriage. Informed that Enrico still hates him, Edgardo reflects on the wrongs suffered by his family at the hands of the Ashtons. He declares that only his love for Lucia has stopped the vengeance which, on his father’s tomb, he had sworn to wreak. Lucia implores him to forget his old hatred, while Edgardo asks her to swear eternal faithfulness. They exchange rings and part 

A study in Lord Ashton’s apartments. Enrico, who is waiting for Lucia, talks to Normanno. The relatives have arrived at the castle for the marriage of Lucia to Lord Arturo. But Enrico still fears his sister’s refusal. Normanno reassures him: Edgardo has been away a long time, and the false rumours artfully put about have it that he is married to another woman. Lucia arrives, looking pale and expressionless. Enrico shows her a false letter, proving Edgardo’s betrayal. He then insists that his sister marry Arturo, thereby saving the family fortunes. With a sinking heart, Lucia seeks comfort from Raimondo, who invites her to accept marriage. At last, indespair, she submits to her brother’s wishes.

A magnificent hall pompously adorned. Arturo promises his political support to Enrico. The wedding ceremony begins. Lucia has just signed the marriage register when, to everyone’s astonishment, Edgardo suddenly appears, still wearing the clothes he has travelled in. Raimondo shows him the marriage contract . Edgardo returns the ring received from Lucia, who is prostrate and incapable of any reaction. He asks her to give him back his own ring, which he flings onto the floor, cursing the Ashtons. He then offers himself, furious and unarmed, to his enemies. 

A ground floor hall in the Wolferag tower. It is night, and a fierce storm is raging. Edgardo is in a gloomy mood. Enrico arrives announcing the completion of Lucia’s marriage and challenging him to a duel. They agree to meet outside the castle, at the Ravenswood graveyard. 

A gallery in Ravenswood Castle. At the castle in the meantime the wedding celebrations continue. But Raimondo interrupts the revelry with news that Lucia has gone mad and stabbed the bridegroom to death. The bride herself now comes onto the scene, dressed in white, disheveled and looking like a ghost. She talks deliriously, recalling her encounters with Edgardo in the belief that he is her husband. Finally, she faints into Alisa’s arms. While Enrico bemoans his wretched state, Raimondo accuses Normanno of having brought about these misfortunes and prophesies that the blame for the blood spilt will fall upon him. Outside the castle, in the Ravenswood graveyard. Edgardo awaits Enrico, having decided to let himself be killed in the duel. He is obsessed by visions of Lucia happy with her newlywedded husband. But from the castle comes the sound of voices announcing Lucia’s death. In desperation, Edgardo stabs himself.