Some time ago, Lord Enrico Ashton had seized power from the Ravenswood family and killed the head of the family – Edgardo’s father. When a new monarch ascends the throne, however, Enrico suddenly finds himself a member of the politically persecuted side and must fear for his life. To save himself, he determines to arrange the marriage of his sister Lucia, whom he has shielded from the outside world, to the influential Lord Arturo Bucklaw. When he informs his close friends of this, Raimondo, Lucia’s tutor, reminds him how much Lucia is still grieving for her recently deceased mother and is therefore not capable of even considering marriage. To his great dismay Enrico then learns from his captain Normanno that, despite her loss, Lucia has in the meantime fallen head over heels in love with a man she does not know but who saved her from being attacked by a raging bull. Furthermore it turns out that this unknown man is none other than Enrico’s mortal enemy, Edgardo. Boiling with anger, Enrico swears bloody revenge.
As the mentally delicate Lucia awaits her rendezvous with Edgardo, she tells her companion Alisa of a frightening apparition in which Lucia believes she saw the ghost of the woman who was murdered by a Ravenswood in a fit of jealousy and then thrown into the well. However, her love for Edgardo and the prospect of his imminent arrival soon brighten her mood. Edgardo rushes in shortly thereafter, only to take his leave of Lucia as he must leave immediately for France. Lucia is alarmed at his plan to try and reconcile with Enrico before he leaves and persuades him to abandon it; their love should remain a secret. As they bid farewell to each other, the two quickly exchange rings as a token of their vow of love.
During Edgardo’s long absence, all his letters to Lucia are intercepted by Enrico and Normanno and replaced by forgeries. Thus misled, Lucia is persuaded of Edgardo’s infidelity and submissively agrees to marry Arturo. Since in spite of everything Lucia wants to remain faithful to Edgardo, Enrico emphasizes to his sister that her refusal to marry Arturo would mean the downfall of their family. When Raimondo finally admonishes her to submit so that her dead mother can rest in peace, in desperation Lucia agrees, but at the same time longs for death.
At the celebrations for her wedding to Arturo, Lucia, already starting to lose her mind, must be urged to sign the marriage agreement. Scarcely has she done so when Edgardo unexpectedly enters the room to demand his rightful place at Lucia’s side. However, when he learns that the young woman has already sealed her marriage to Arturo with her signature, in despair he gives Lucia’s ring back to her and flees to his estate at Wolf’s Crag. A storm is brewing. Furious, Enrico leaves the wedding and in the middle of the night seeks out his rival in his tower at Wolf’s Crag. Driven by hatred, vengeance and jealousy, the two men agree to fight a duel at daybreak at the Ravenswood tombs.
In the meantime, losing her senses Lucia has stabbed Arturo in the bridal chamber. In a state of complete mental disarray, she enters the ballroom, still filled with guests. In a vision she first sees her marriage to Edgardo and begs her lover, who is not present, to forgive her and to mourn at her grave. With his sister’s madness now evident, the returning Enrico realizes too late that he is to blame.
Edgardo awaits the duel with Enrico at the tombs of the Ravenswoods. He learns from several passers-by that Lucia has lost her mind, is on her deathbed and is asking plaintively for him. Edgardo sets out immediately to see his beloved one more time, but Raimondo comes to meet him and confirms that she has already died, as signalled by the chiming death knell. In the hope of being finally united with Lucia, Edgardo stabs himself.