The hero is Siegfried and the heroin is Kriemhild. Siegfried wants to marry the sister of Gunther but the only way to get the consent of the king of Burgundy is to help Gunther to win the heart of queen Brunhild. And Gunther gets what he wanted and a double wedding happened.
The ceremony ended but the sadness in face of queen Brunhild. Little that Gunther knows queen Brunhild admires Siegfried and has a feeling for the hero. Things have been worse between Gunther and Brunhild and Siegfried pities Gunther so the king tells the secret of Brunhild's strength.
Siegfried succeeds and lives a life with his beloved wife. But the queen didn't stop and vows vengeance with the loyal vassal of Gunther which is Hagen. They planned to kill Siegfried.
They come up to the story that enemies are gonna attack the kingdom and as the hero, Siegfried volunteers to defend the kingdom. Hagen asks Kriemhild where is the vulnerable spot of Siegfried so that he can protect it from enemies. The wife said it and afterward the army and Siegfried hunt down and take a little break. That's the time that Hagen had his chance to kill Siegfried.
Kriemhild, the beloved wife of Siegfried, didn't accept the death of his husband. She want revenge and to do that successfully, she married the king of Huns, King Etzel. The king asks her kinsmen, including Hagen to go to a bloody battle.
In the end, Gunther, And Hagen are taken to prisoners and put to death by Kriemhild, who herself killed in the end.