Enrico visits Edgardo to challenge him to a duel. He tells him that Lucia is already enjoying her bridal bed. Edgardo agrees to fight him. They will meet later by the graveyard of the Ravenswoods, near the Wolf's Crag.
Scene 2: A Hall
Raimondo interrupts the marriage celebrations to tell the guests that Lucia has gone mad and killed her bridegroom Arturo. Lucia enters. In the aria 'Il dolce suono' she imagines being with Edgardo, soon to be happily married. Enrico enters and at first threatens Lucia but later softens when he realizes her condition. Lucia collapses. Raimondo blames Enrico for precipitating the whole tragedy.