A family feud has waged between the Ashtons and the Ravenswoods since the recent Civil War, a period which has enriched the middle classes, whilst the aristocracy has grown poor. The recently ennobled Enrico Ashton has managed to lay his hands on the castle and estates of the Ravenswoods, and Edgar, the last of the family, is living in the Wolfscrag, a half-ruined tower. There he broods over the wrongs that he believes have been done to his family. Unknown to Edgardo, a change of power means that his case will probably be re-opened, and it is possible that the Ashtons will lose the castle and estates. In order to prevent this, it is essential that the family ally themselves with the powerful faction by marriage to Lord Arturo Buklaw.
The followers of Ashton are searching the woods for a trespasser. Normanno suspects that it is Edgardo, and suggests they go looking in the direction of the Wolfscrag. Enrico is afraid that Lucia, his sister, will refuse to marry Arturo. Raimondo, the Ashtons’ Chaplain, suggests she is still mourning the recent death of her mother. Normanno mentions that she has been seeing a young man who saved her life, and suggests that he might be Edgardo. Enrico proclaims that a connection with his enemy would be worse than death, and when his men return with the news that the stranger was Edgardo, he swears revenge.
Lucia is waiting for Edgardo. The fountain has a legend attached to it which Alisa, Lucia’s maid tells her. A Ravenswood had stabbed his unfaithful wife near here. Lucia tells how while out walking she saw her ghost. It disappeared into the fountain which turned blood-red. When Edgardo arrives, he tells her that he is leaving on an important mission for Scotland. Beforehand, he wishes to make peace with Enrico and ask for her hand in marriage. She makes him promise to keep their love a secret. They swear eternal love, and Edgardo promises to write to her from abroad.
Enrico is waiting for Lucia. He still fears that his plans may be upset. Normanno calms him and reminds him that not only have all Edgardo’s letters been intercepted, but also he has forged a letter which suggests that Edgardo has been unfaithful. Lucia is very upset when she read the letter. Preparations for the wedding are started. Enrico begs Lucia to help him since she has lost Edgardo. Raimondo tells Lucia that he had sent a message to Edgardo via a reliable messenger, but he has had no reply. Since the oath she swore with Edgardo was not in a church, it may be ignored. She agrees to marry Arturo.
The guests receive Lord Arturo Buklaw, who feels himself to be Enrico’s saviour. Lucia appears in bridal clothes. Enrico excuses her woeful appearance by explaining that she is mourning her mother. While her brother whispers threats, she signs the marriage contract as though it were her death warrant. Edgardo appears. Raimondo just manages to prevent a duel between Edgardo and Enrico. When he sees Lucia’s signature, Edgardo curses her and the house of Ashton.
A storm is raging. Enrico arrives and challenges Edgardo to a duel. They agree to fight the next morning near the Ravenswood family tombs.
While the guests are celebrating the wedding, Raimondo enters with the news that Lucia has killed Arturo and gone mad. She appears. Firstly she believes that she sees the ghost of the fountain, and then she imagines she is going through a marriage ceremony with Edgardo. She begs him to forgive her, and promises to pray for him in Heaven. Enrico realises he has driven his sister mad, while Raimondo accuses Normanno of being responsible.
Edgardo is waiting for Enrico. He intends to die in the duel. Passing guests report the terrible events, and say that Lucia is dying. A bell is heard. Edgardo longs to see her one last time, but Raimondo announces that she is already dead. He stabs himself.