Act One:

King Henry orders his fellow Germans to drive the Hungarians out of his realm upon his arrival in Brabant. The young Duke Gottfried has disappeared. His sister, Elsa, is accused of killing him by Count Telramund, their former guardian. His conniving wife, Ortrud, put this idea in his head because she wants him to take over as duke. Elsa declares her innocence and recommends a duel as means to prove it. King Henry encourages Telramund to accept the offer. Elsa prays for the knight who appears to her in dreams to save her. Miraculously, a boat appears on the river, drawn by a swan. Elsa's knight in shining armor has arrived! He asks Elsa if she will have him as her champion, to which she replies gratefully. His only condition is that she never asks him who he is or where he's from. Elsa agrees and the duel takes place. The knight wins, spares Telramund's life, and he proposes to Elsa.

Act Two:

Telramund and Ortrud, despite having been banished, appear in the courtyard outside the cathedral just hours before the wedding. Ortrud, a pagan sorceress, is determined to bring about Elsa's demise. To add salt to the evil couple's wound, the king has made the knight the Duke of Brabant. The knight refuses the title and asks that he only be known as Guardian of Brabant. Ortrud plots to make Elsa ask the knight the two questions she promised she never would. As everyone heads into the cathedral, Ortrud appears and accuses the knight of being an evil magician. Telramund claims to have been banished by fraud because he doesn't know the name of the knight. The knight refuses to reveal his identity.

Act Three:

Now married and in their chamber, Elsa and the knight express their love for each other. Curiosity is getting the best of Elsa and she asks the fatal question: who are you? Just then, Telramund bursts into the room and tries to kill the knight, only to be fatally wounded. The knight sadly asks Elsa to come with him to meet with the king, where he will answer her question. On the banks of the river, troops arrive ready for war. Telramund's corpse is brought before the king and the knight defends his honor. He then reveals his identity as Lohengrin, knight of the Holy Grail, and son of King Parsifal. He must now return to his castle. As he says goodbye, he prays that Elsa finds her missing brother. The swan reappears, dives into the river, and emerges as Gottfried. He had been turned into the swan by Ortrud's magic, in her attempt to help Telramund seize the dukedom. A dove flies from the heavens to lead Lohengrin back to the castle of the Holy Grail.