In the third act Ethelerus holds council with magister Rhynperg as to the means, by which they can best succeed in teasing and provoking the proud Sunneborn. Hunold enters, and agreeable to an invitation of theirs, sits down to drink a bottle of wine. They make him drink and sing a good deal, and he boasts of being able to make the maidens all fall in love with him, if he chooses. Rhynperg suggests that he must omit the Burgomaster's daughter Regina, and he succeeds in making Hunold accept a wager, that he will obtain a kiss from her before his departure.
The following night Hunold accomplishes the exorcism of the rats, which may be seen running towards him from every part of the town and precipitating themselves into the river. Unhappily, Wulf, standing in a recess, has seen and heard all and coming forward to threaten Hunold, the latter hurls his dagger after him, upon which Wulf takes flight.
In the fourth act the whole town is assembled to rejoice in its deliverance from the awful plague, but when Hunold asks for his reward, the Burgomaster tells him, that a so-called rat-king, a beast with five heads, has been seen in his (the Burgomaster's) cellar, to which complaint Hunold replies, that it is the smith's fault, who listened against his express prohibition. He promises to destroy the rat-king on the same day and once more claims his due, together with the promised parting gift, which he begs to be, not a drink of wine, but a kiss from Regina's lips. Of course everybody is astounded at his insolence, and the angry Burgomaster bids him leave the town at once, without his money. But Hunold, nothing daunted, begins to sing so beautifully that the hearts of all the women yearn towards him, he continues still more passionately, addressing himself directly to Regina, and never stops, till the maiden, carried away by a passion unconquerable, offers her lips for a kiss, swearing to be his own for ever. A great tumult arises and Hunold is taken to prison, notwithstanding the remonstrances of Ethelerus, who bitterly repents having had anything to do with Rhynperg's bad joke.
The fifth act takes us to the banks of the Weser, where Gertrud sits in despair. She deems herself betrayed by Hunold, but resolves nevertheless to save his life.
Hunold is brought before the judges and condemned to be burnt alive as a sorcerer, when Gertrud steps forth, claiming his life. In pursuance of an old privilege, Hunold is free when a maid of the town claims him, but he is banished from the country and Gertrud with him.
Hunold promises never to return, but Gertrud throws herself into the river.
Then Hunold swears to avenge the death of his bride. While the citizens are in church, he lures away their children by playing on his pipe; all follow him, both great and small. When he has led them safely over the bridge, he calls the people from church. All gather on the banks of the stream, but they are only just in time to see the bridge fall into the river, while the mountain opposite opens, swallowing up Hunold and the children for ever.