La donna del lago by Giacomo Rossini

The Lady of the Lake is set in Scotland. The Highlanders and King James’s former tutor, Douglas, have turned against their ruler. Douglas’s daughter, Elena, is in love with Malcom, but has been betrothed to marry Rodrigo, the leader of the Highlanders.
King James has disguised himself as Uberto and is seeking the legendary beauty, Elena. They meet at the lake and Elena offers the “lost hunter” shelter in her home. King James/ Uberto then learns who her father is, and that she is betrothed, which arouses his jealousy. When he sees Elena does not love Rodrigo, he leaves (still in disguise), with hopes that she may be his.
Malcom arrives to join the Highlanders and witnesses Douglas ordering Elena to marry Rodrigo, despite her reluctance. The two declare their love for each other. Rodrigo then arrives, eager to see his bride, but it becomes clear she has feelings for Malcom. As news arrives of a looming attack by the King, Rodrigo, Malcolm and the Highlanders prepare to head into battle.

King James/ Uberto returns to take Elena to safety before the battle. He declares his love for her, but she tells him she loves another. He gives her a ring, supposedly a gift from the King, as a guarantee of safe passage. Rodrigo has overheard “Uberto’s” declaration of love and orders his men to kill Uberto. Elena pleads with the soldiers but Rodrigo challenges “Uberto” to a duel and they both leave.

Meanwhile, Douglas has set off to the King’s palace to try to make peace. Elena follows him, and Malcom, in turn, follows her, wishing to protect his beloved from danger. (Unbeknownst to Elena, Rodrigo has been killed and his Highlanders face defeat.)
The King refuses to forgive Douglas his betrayal. Elena gains entrance to the palace using the King’s ring. When she hears “Uberto” singing of his love for her, she hopes he will help her intercede with the King and save her father and Malcolm. On entering the throne room, she realises “Uberto’s” true identity. King Kames, moved by his affections for Elena, forgives Douglas and Malcolm. Peace is restored and Elena’s happiness knows no bounds.