ACT I. In a ruined park near Lammermoor Castle, Enricos retainers prepare to search for a mysterious trespasser. Normanno, captain of the guard, remains behind to greet Enrico, who decries Lucias refusal to marry Arturo. When the girls elderly tutor, Raimondo, suggests that grief over her mothers death keeps her from thoughts of love, Normanno reveals that Lucia has been discovered keeping trysts with a hunter who saved her from a raging bull. He suspects the stranger is none other than Edgardo. Enrico rages, and as retainers confirm Normannos suspicions, he swears vengeance.

At a fountain near her mothers tomb, Lucia, fearful of her brother, awaits a rendezvous with Edgardo. She tells her confidante, Alisa, the tale of a maidens ghost that haunts the fountain and has warned her of a tragic end to her love for Edgardo. Though Alisa implores her to take care, Lucia cannot restrain her love. On arrival, Edgardo explains he must go to France on a political mission but wishes to reconcile himself with Enrico so he and Lucia may marry. Lucia, knowing her brother will not relent, begs Edgardo to keep their love a secret. Though infuriated at Enricos persecution, he agrees. The lovers seal their vows by exchanging rings, then bid each other farewell.

ACT II. In an anteroom of Lammermoor Castle, Enrico plots with Normanno to force Lucia to marry Arturo. As the captain goes off to greet the bridegroom, Lucia enters, distraught but defiant, only to be shown a forged letter, supposedly from Edgardo, proving him pledged to another. Crushed, she longs for death, but Enrico insists on her marrying at once to save the family fortunes. Now Raimondo urges her to consent to the wedding, invoking the memory of her mother and asking her to respect the familys desperate situation. When she yields, he reminds her there are heavenly rewards for earthly sacrifices.

In the great hall of Lammermoor, as guests hail the union of two important families, Arturo pledges to restore the Ashtons prestige. Enrico prepares him for Lucias melancholy by pleading her grief over her mothers death. No sooner has the girl entered and been forced to sign the marriage contract than Edgardo bursts in. Returning earlier than expected, he has learned of the wedding and come to claim his bride. Bloodshed is averted only when Raimondo commands the rivals to put up their swords. Seeing Lucias signature on the contract, Edgardo tears his ring from her finger, curses her and rushes from the hall. Hardly comprehending his words, Lucia collapses.

ACT III. Edgardo sits in a chamber at the foot of Wolfs Crag tower, deep in thought, as a storm rages. Enrico rides there to confront him, and the flames of their enmity flare. They agree to meet at dawn among the tombs of the Ravenswoods to fight a duel.

The continuing wedding festivities are halted when Raimondo enters to announce that Lucia, gone mad, has stabbed and killed Arturo in the bridal chamber. Disheveled, unaware of what she has done, she wanders in, recalling her meetings with Edgardo and imagining herself married to him. When the angry Enrico rushes in, he is silenced by the sight of her pitiful condition. Believing herself in heaven, Lucia falls dying.

Among the tombs of his ancestors, Edgardo, last of the Ravenswoods, laments Lucias supposed betrayal and awaits his duel with Enrico, which he hopes will end his own life. Guests leaving Lammermoor Castle tell Edgardo the dying Lucia has called his name. As he is about to rush to her side, Raimondo arrives to tell of her death, and her bier is carried by. Resolving to join Lucia in heaven, Edgardo stabs himself and dies.