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Composer Carl Maria von Weber is pictured here in about 1820, two years before he wrote Euryanthe.
ACT ONE: The opera opens in King Louis' castle. At a celebration of peace, Count Adolar sings a romance in tribute to Euryanthe, his bride. Everyone joins him in praising her, except for Count Lysiart. Instead, Lysiart proposes a bet with Adolar, saying that he can prove that Euryanthe is unfaithful. The loser will forfeit all of his lands. Adolar accepts the wager.
The next scene, at Adolar's castle, finds Euryanthe with Eglantine — who is also in love with Adolar, and secretly hates Euryanthe. Eglantine has seen Euryanthe behaving strangely at night, and thinks she's hiding something. Pretending loyalty to Euryanthe, Eglantine persuades her to reveal a secret.
Euryanthe says the ghost of Adolar's dead sister, Emma, has appeared to her and admitted that, after her lover was killed in battle, she committed suicide with poison contained in her ring . The ghost cannot rest until the ring has been washed by the tears of an innocent young woman. Every night, Euryanthe has been praying in her tomb that Emma's spirit can, finally, rest in peace.
Euryanthe feels guilty about revealing all this, but Eglantine reassures her, declaring her loyalty, and says the secret is safe. But when Euryanthe leaves, Eglantine is furious, and makes plans to denounce Euryanthe to Adolar.
Before long, Lysiart arrives. He's greeted by the people of the countryside and by Euryanthe. Watching Lysiart, Eglantine can see that he's in love with Euryanthe, and decides to ask Lysiart for help with her plot.
ACT TWO: Late at night, Lysiart is alone in Adolar's castle, wavering between guilt and desire. Finally, he decides to pursue his dishonest agreement with Adolar. Lysiart has wagered all his lands against Adolar's, betting he can prove that Euryanthe is unfaithful.
Meanwhile, Eglantine has entered Emma's tomb, and emerges after removing the poison ring from Emma's corpse. She's met by Lysiart, who proposes an alliance and marriage. They seal their pact in a duet.
The next scene is at King Louis' hall, where Adolar sings an aria, longing for Euryanthe. Euryanthe hurries in, and the two profess their love. When the two are welcomed at the King's court, Lysiart comes forward to claim victory in his wager with Adolar.
Lysiart has Emma's ring, given to him by Eglantine. When he says that he knows the secret of the tomb, and produces the ring as proof, it seems he must have gotten the ring, and the secret, from Euryanthe. This convinces everyone that Euryanthe has betrayed Adolar, and Lysiart wins the bet. Adolar forfeits his lands, and leads Euryanthe off to wander in the wilderness.
ACT THREE: Adolar and Euryanthe are in a mountain gorge. Adolar still believes that Euryanthe has betrayed him, and plans to kill her.
As Euryanthe claims her innocence, a poisonous snake appears. Euryanthe steps between the snake and Adolar to protect him. Adolar quickly dispatches the snake, but he's moved by Euryanthe's willingness to sacrifice herself for him. So, instead of killing Euryanthe, he says he'll simply abandon her.
Alone in the next scene, Euryanthe says that she welcomes death, and hopes that Adolar will eventually know that she never was unfaithful to him. She then hears horns coming through the woods. The king approaches with his hunting party, surprised to find Euryanthe alone in the mountains. In a duet with chorus, Euryanthe tells the king everything that has happened, and convinces him that she's innocent.
Back at Adolar's castle, the local people sing a May song as Adolar approaches in the distance. When the people recognize him, they reveal the scheming of Lysiart and Eglantine, and tell him that Euryanthe has been vindicated. They pledge their support and urge Adolar to punish the traitors.
Lysiart and Eglantine approach in apparent triumph, to the sounds of a wedding march — but the people curse Lysiart. When he and Adolar confront each other, the king arrives in time to prevent violence.
In the final scene, the king tells Adolar that Euryanthe's heart is broken. When Eglantine mocks Lysiart for failing in his part of their bargain, Lysiart stabs her to death, and is led away. To the sound of hunting horns, the rest of the king's party arrives, escorting Euryanthe. Her tears have washed the poison from Emma's ring. Now Emma's spirit can finally rest, Eurythanthe and Adolar can be together, and the opera ends with a joyful chorus.