Scotland, seventeenth century. Henri Ashton explains to his confidant Gilbert that, for political reasons, he has decided to marry his sister Lucie to Arthur Bucklaw, the powerful Lord Athold’s nephew. However, Lucie is in love with Edgar Ravenswood, the last member of the Ashtons’ rival family. Gilbert informs Henri of a secret rendezvous between Lucie and Edgar. Then comes Arthur, and he is reassured by Henri about Lucie’s love for him. In any case, Arthur says, his uncle has ordered Edgar to go to France on a diplomatic mission. Pretending to be her friend, Gilbert accompanies Lucie to the place where she is to meet Edgar. While she waits for him, Lucie laments that the old hatred between the two families makes their love impossible. Edgar arrives bearing the sad news that is about to leave. But, before that, he asks Henri for his sister’s hand. The two lovers exchange rings and bid farewell.
Gilbert has followed Edgar to France, intercepted his letters, and made a copy of the ring Lucie had given him. Back in Scotland, he reports everything to Henri, who is even more determined to conclude the marriage with Arthur. In a dramatic confrontation, Henri tells Lucie that Edgar no longer loves her, shows her the ring, and tells her that only her marriage to Arthur can save him from political disgrace. Lucie surrenders. Accompanied by a festive choir, Arthur arrives and, as Lucie despairs, the wedding ceremony begins. The marriage contract has just been signed when Edgar bursts in, challenging Henri and Arthur. Raymond, the chaplain, prevents the confrontation and shows Edgar the signed contract. Believing that Lucie has betrayed him, Edgar curses her.
Gilbert informs Henri that a man has come looking for him. It is Edgar in disguise, who challenges his enemy to a duel: they fight at dawn. Meanwhile, as the wedding party is taking place at the Ashton castle, Raymond suddenly interrupts it and brings terrible news: Lucie has lost her mind and killed Arthur. Lucie appears, maddened, raving about her love for Edgar, about her curse, and proclaims that she will soon die. In the meantime, Edgar is waiting for Henri at the scene of the duel. The chorus informs him that Henri will not come and that within an hour Lucie will be dead, then reveal that the woman has always been faithful to him. Edgar is distraught and invokes Lucie for the last time, stabs himself, and dies in Raymond’s arms.