The action takes place at the Ravenswood family estate, now owned by the Ashton family. 

Overture

The Ashton family are searching for an intruder on their grounds. Normanno suspects he is in the Ravenswood family crypt and hides himself there. Edgardo Ravenswood, the intruder, arrives and delivers a letter for his lover, Lucia Ashton. Alisa, Lucia’s maid and companion, delivers Lucia’s love letter, and is surprised to discover Edgardo’s. Normanno finds Lucia’s letter, and calls for Enrico Ashton and the other men to join him in the crypt.

Lucia is in mourning for her mother. She brings her mother’s urn to her closet, and writes a letter to her secret lover. She calls Alisa, to deliver the letter.

ACT I  

SCENE 1

Back in the crypt, Normanno and other men discuss catching the intruder (Percorrete le spiagge vicine). Enrico explains to Normanno that his family fortunes are in jeopardy: to recoup them, he needs to persuade his sister Lucia to marry Arturo Bucklaw, a wealthy local gentleman. Enrico’s chaplain Raimondo Bidebent reminds his master that Lucia has no desire to marry, and is still mourning the death of their mother. Normanno hints that in fact Lucia loves Edgardo, a penniless nobleman who saved her from being attacked by a bull. Enrico, who hates Edgardo, is furious (Cruda, funesta smania) and vows to destroy his enemy (La pietade in suo favore).

Alisa returns to Lucia’s closet with Edgardo’s letter, but she and Lucia are interrupted by Enrico and Raimondo before they can read it. A footman arrives to bring Enrico to the crypt. Lucia reads Edgardo’s letter, in which he urgently asks to meet her that night. She and Alisa disguise themselves as men.

SCENE 2

Lucia, in disguise, is waiting for Edgardo in the crypt. She tells Alisa that she has recently seen the ghost of a Lammermoor girl murdered by one of Edgardo’s ancestors (Regnava nel silenzio). Alisa suspects that this is an ill omen and urges Lucia to end her relationship with Edgardo, but Lucia’s love is too strong for this (Quando rapito in estasti). 

Edgardo arrives, and tells Lucia that he will depart the next day. He wants to get Enrico’s permission for him to marry Lucia before he leaves. Lucia, worried about her brother’s ferocious temper, forbids him to do this. Instead, the lovers exchange rings and swear to be faithful. Lucia asks Edgardo to write to her while he is away (Verranno a te sull’aure). 

Meanwhile, Enrico and Normanno search Lucia’s room and closet for more evidence of the secret affair.

ACT II

SCENE 1

Normanno has intercepted Edgardo’s letters to Lucia, and forged one to say that Edgardo now loves another woman. Enrico hopes this will make Lucia accept Arturo Bucklaw. Lucia informs Enrico that his cruel behaviour has hurt her (Il pallor funesto). She refuses to marry Arturo, and tells Enrico that she considers herself Edgardo’s wife. Enrico hands her the forged letter. Lucia is devastated, and Enrico and Raimondo pressure her to accept Arturo’s offer; Raimondo tells Lucia that her exchange of rings with Edgardo had no legal validity, and urges her to remember her family duty, particularly her obligation to her dead mother (Ah! cedi, cedi). Lucia at last agrees to the marriage, and Raimondo reassures her that Heaven will reward her.

In her bathroom, Lucia, now three months pregnant with Edgardo’s baby, has morning sickness.

ACT II 

SCENE 2

Back in the closet, Alisa dresses Lucia for her wedding. Later, Edgardo breaks into the house through the open window.

In the banquet hall, the wedding guests welcome Arturo as Lucia’s bridegroom, and he promises to restore the Ashton family fortunes. Enrico warns Arturo that Lucia is still grieving for their dead mother, and may appear upset. When Lucia arrives, Enrico forces her to sign the marriage contract. As she does so, Edgardo bursts in. Everyone is shocked (Chi mi frena in tal momento). Edgardo threatens Arturo and Enrico, and is only prevented from fighting them by Raimondo, who shows Edgardo the marriage contract. When Edgardo realizes that Lucia has married Arturo, he tears his ring from her finger and curses her. Lucia despairs.

INTERVAL

ACT III 

SCENE 1

Lucia, unable to go through with the marriage, plots with Alisa to murder Arturo. Arturo arrives for his wedding night, and is murdered by the two women in the bedroom.

Back in the banquet hall, Edgardo, held by Normanno, waits for Enrico. When he arrives, Enrico taunts his enemy about Lucia’s marriage (Qui del padre ancor respira) and challenges Edgardo to a duel the following day at dawn.

SCENE 2

Raimondo, drawn by the screams, catches Lucia and Alisa with Arturo’s body. While Normanno guards the two women, Lucia has a miscarriage.

In the billiard room, the festivities for Lucia’s wedding (D’immenso giubilo) end abruptly when Raimondo announces that Lucia is mentally unstable and has murdered Arturo. Lucia, confused after killing her husband and suffering from her miscarriage, believes that she is about to marry Edgardo; she recalls their earlier meetings and her encounter with the ghost of her ancestor, and prepares for her wedding ceremony (Il dolce suono... Ardon gl’incensi). When Enrico sees her, he is initially furious, but when he hears his sister declare herself the victim of his cruelty, he is moved to compassion. Lucia tells Edgardo (who she believes to be present) that she is dying, and will wait for him in Heaven.

SCENE 3

In the crypt, Edgardo, still believing Lucia has betrayed him, reflects bitterly on her marriage, and longs for death (Tombe degli avi miei... Fra poco a me ricovero). Men leaving Lucia’s home inform him that Lucia is dying, and has asked to see him. However, it is too late – Raimondo arrives to tell Edgardo that Lucia has died. Edgardo determines to join her and is led to her by Alisa. Enrico arrives, and is accused of cruelty by Raimondo.

Lucia kills herself in her bathroom. On seeing his sister’s body, Enrico is filled with remorse. Edgardo arrives to spend his last few minutes with the body of his loved one (Tu che a Dio spiegasti l’ali), and then takes his own life by her side.