The suppliants of Mokanna, the Veiled Prophet, are gathered in a hall in his palace. His slave Abdullah brings news of defeat at the hands of the Caliph Mahadi. Mokanna appoints the warrior Azim to lead an army against the enemy. The scene changes to the harem, where the priestess Zelica watches the troops making ready and recognises Azim as her former beloved. Mokanna appears and is revealed to Zelica as a demon, but he reminds her that they are joined by an eternal oath. The second act takes place in the harem, where the chief slave Fatima and the other women are preparing to receive Azim. Abdullah leads him in and Azim finds himself alone, but Zelica enters and the lovers are reunited. He persuades her to flee with him, but Mokanna intercepts them. Azim’s sword breaks on the demon’s body, and he runs off. The final act takes place at night in the besieged city, where the disaffected populace is preparing to revolt. Mokanna reveals himself among them, and demonstrates his power by apparently causing the moon to rise. They are convinced, and Mokanna invites them into the palace to drink with him -- but the cups are poisoned. Zelica and Fatima enter, awaiting rescue by Azim. Fatima leaves, and Zelica sings of her hope, but is brought up short by the groans of Mokanna’s victims dying in the palace. The Prophet now descends and offers Zelica a fatal cup, which she refuses. As dawn breaks Azim rushes in to protect Zelica. As he and Mokanna wrestle on the ground the gates are opened and the Caliph’s army enters. Rather than be captured, Mokanna stabs himself.