Lord Ullin is a very angry man. His daughter has run off with a chieftain—the Chief of Ulva's Isle, no less—and he and his men are in hot pursuit. If they should catch up with the eloping lovers, there's no telling what they'll do to them. Understandably, the Chief and Ullin's daughter are keen to get away, and they hastily instruct a ferryman to take them to the other side of Lochgyle, even though the water is dark and stormy. As the sound of Lord Ullin's men and their horses gets nearer and nearer, the storm becomes ever more violent.
Lord Ullin finally reaches his daughter on the far side of Lochgyle. But this shore is a "fatal shore," for Lord Ullin's daughter and her lover lie dead. Lord Ullin's anger turns to sorrow, and he loudly laments his loss as the waves crash against the shore. In retrospect, there was very little he could've done to save his daughter after she boarded the ferry. Once she was out on the loch in the middle of such a terrible storm, it would've been suicide for him to attempt any kind of rescue. But perhaps if he'd controlled his anger in the first place, then maybe his daughter wouldn't have eloped with her lover, and both of them might still be alive.