The scene is laid on the island of Thule (otherwise Germany, perhaps Ruegen), at the time after the destruction of Carthage.
In the first Act Hiram, a Carthaginian priest emerges from a cave, where he has found a refuge. He has brought Carthage's famous idol Moloch to Thule, with the intention of subjecting the inhabitants to its power, in which he himself no more believes since the downfall of his native city.
The inhabitants of Thule do not as yet worship any particular god, and Hiram hopes to gain enough ascendancy over them, to use them as a means of revenge against Carthage's great enemy Rome.
When the people of Thule catch sight of the fearful idol, they are frightened, and Hiram intensifies their terror by taking advantage of natural causes. A terrific thunderstorm comes on and the lightning striking the hollow brass figure, sets light to the wood inside and makes the figure become red hot.
The King's son Teut is one of Hiram's first converts. Moloch, he says, has appeared to him in his dreams, and in spite of the remonstrances of Wolf, his father's friend, in spite of Theoda's and his mother's tears, he worships at Moloch's feet together with the majority of his followers.
Velleda, his mother, a somewhat mystic personage, who foresees every misfortune, prophetically sees her son in the fearful monster's jaws; she veils herself shuddering and withdraws into the woods.
Theoda, who loves Teut hopelessly tries all her simple wiles and allurements on him in vain. When Hiram sacrifices a pair of doves and a ram to the idol, the people all join in his exulting cry of "Moloch is King, he is Lord over all", with which grand and impressive chorus the first Act closes.
The second Act takes place near the sacred yew of the Thuleans. Wolf meets Theoda, and tells her, that Teut is alienating the people with the new religion, and that he must be slain. Theoda opposes him, but he turns from her, and goes to summon the old King to pronounce judgment.
Meanwhile Hiram approaches the yew, accompanied by the labourers, who are returning from their work. He has taught them to plough the ground, to sow, to till the soil, and now he deems it time to fell the old tree, which they have hitherto held sacred, and under the branches of which the King is wont to pronounce judgment.
Hiram is about to lay the axe to its roots, when the King appears. Seeing his son bearing a foreign sword, he bids him lay it down at his feet. But Teut declares, that he has received the sword for the protection of Moloch, and audaciously summons his father to dedicate his own ancestral weapon to the new god.