ACT I
King Henry's Saxon army marches into the Duchy of Brabant on the banks of the Scheldt. The leaderless neighboring country is to join Henry's campaign against the Hungarians. However, the question of succession in the duchy must first be decided. Henry favors Count Frederick of Telramund. He accuses Elsa of Brabant, the first-born daughter of the deceased duke, of having drowned her younger brother Gottfried, the heir to the throne. Elsa is summoned to court. Instead of defending herself, she conjures up the image of an unknown knight who will prove her innocence in a court of God, marry her and succeed her father.
The appeal of a defender who would be prepared to fight Frederick of Telramund "to the death" initially goes unanswered until an unknown man approaches across the water, whose strangeness casts a spell over everyone. After an address of loyalty to King Henry and before he faces the duel with Frederick of Telramund, Elsa must promise him never to ask his name and identity, whereupon he declares his love for her. The subsequent judgment of God decides against Frederick of Telramund. Brabants and Saxons cheer the Nameless One.
ACT II
Only Ortrud, the wife of Friedrich von Telramund, doubts the divine legitimacy of the Nameless One. The outsider, who has not converted to Christianity, claims to have witnessed Elsa's murder of Gottfried. She persuades her husband, who has been declared outlawed, to attempt to disenchant the Nameless One: she herself will manipulate Elsa into asking the forbidden question after all, he should publicly accuse the Nameless One of sorcery; even if she succeeds in seizing a limb of his body, however small, his power would be broken. Ortrud succeeds in being accepted back into Elsa's grace.
The Nameless One has himself declared 'Protector of Brabant' and agrees with King Henry that, following his marriage to Elsa, he will lead the Brabant army to war alongside Henry's troops. Fuelled by the belief in the new ruler's divine mission, the general mobilization of Brabant begins at the same time as the wedding preparations.
On the way to the wedding, Ortrud confronts the bride and publicly raises doubts about the identity of the nameless man, before Frederick also questions the legitimacy of God's judgment, as he has failed to establish the name and origin of his rival. The battle-ready Saxons and Brabants are not interested in such a clarification. However, it is only when Elsa publicly declares her own doubts about the "Protector of Brabant" to be overcome that the wedding can take place.
ACT III
Elsa and the Nameless One are led into the bridal chamber. Elsa demands a share in her husband's secret so that she can take conscious responsibility for keeping it, for which she would be prepared to risk her life. The Nameless One refuses, but in return offers her the chance to forgo a precise clarification of the background to her brother's disappearance.
Nevertheless, Elsa asks the forbidden question - regardless of herself or him. At this moment, Frederick of Telramund, who had been in hiding, emerges and is struck down by the Nameless One.
At dawn, the Nameless One declares his resignation before the marching armies of Saxony and Brabant: by asking the forbidden question, Elsa has stripped him of all power, for the success of his mission was linked to the secret of his identity. lnce he now reveals himself as Lohengrin and son of the Grail King, he must withdraw. With his final disappearance, he gives Brabant back the lost heir to the throne, Gottfried.