Early dawn, outside Ravenswood Castle
After an ominous prelude featuring timpani and horns, Normanno, captain of the guard, and his men search for an intruder. Enrico laments his family’s failing fortunes, partially blaming his sister, Lucia, who has refused to marry the wealthy Arturo. Raimondo, a priest, defends Lucia, saying grief over her mother’s death prevents her from welcoming Arturo’s intentions. But Normanno claims that Lucia’s coolness is a result of her secret romance with Edgardo, Enrico’s sworn enemy. Enrico rages at his sister and Edgardo.
Twilight the next day, a fountain
An extended harp solo introduces Lucia and her companion Alisa waiting at a fountain for Edgardo. Lucia says she has seen the ghost of a woman murdered at this fountain by a jealous lover. Alisa fears a bad omen and begs Lucia to give up Edgardo, but she refuses.
Edgardo arrives to tell Lucia that he must travel to France on business. He intends to meet Enrico to settle their differences and ask for Lucia’s hand in marriage, but she insists their relationship remain a secret. They exchange rings, swear eternal love, and part sorrowfully. Edgardo reminds Lucia they are now man and wife.
Months later, a room in Ravenswood Castle
Determined to make Lucia marry Arturo, Enrico and Normanno have intercepted the lovers’ letters and forged one from Edgardo to Lucia in which he says he has fallen in love with another woman. Enrico confronts his distraught sister. She refuses to marry Arturo, and when he shows her the forged letter, she begs God to strike her dead. Raimondo advises Lucia to give in.
Late afternoon the same day, reception hall in the castle
Guests have gathered to celebrate the wedding of Lucia and Arturo. Arturo vows to restore the Ashton family fortunes. Enrico warns him that Lucia might appear melancholy, since she is still in mourning for her mother. As Enrico forces Lucia to sign the marriage contract, Edgardo rushes in, having returned from France when he heard nothing from Lucia. When he sees the signed contract, Edgardo hurls his ring at Lucia, curses her, demands she return her ring, and storms out.
Later that night after the wedding ceremony, great hall in the castle
The guests are still celebrating when Raimondo, deeply upset, interrupts the festivities. He tells them he found Lucia, grasping a knife, standing over Arturo’s corpse. Lucia enters, confused and disoriented. She tells Edgardo that now they are united by heaven. The guests watch in pity and fear.
A few hours later, Ravenswood tombs
Edgardo contemplates joining his dead ancestors. People coming from the castle tell Edgardo that Lucia is near death and calling for him. A funeral knell tolls; Edgardo is determined to see Lucia, but Raimondo tells him she is already dead. Edgardo stabs himself and cries out that God will reunite them in heaven.