The Incas have been at war with the Mexicans. Montezuma has led the Peruvian forces and conquers. Asked by the Inca (the god-king) what he wants, he asks for the king''s daughter''s hand in marriage. He is refused and vows to fight against the Inca, and leaves. Acacis, the captive prince, vows to stay and defend the Inca and his daughter, with whom he is in love.
Back home, thinking him dead, Acacis'' mother Zempoalla takes over and chooses her general Traxalla to be her consort. Then news comes that Acacis lives, and Montezuma, acclaimed as a god of war, rouses the army to go back, by acclaim, to fight. They win the war--the Inca and his daughter flee. Acacis wishes to grant them mercy and honorable safe conduct; Montezuma, to take her as the spoils of war; but Zempoalla has vowed to sacrifice the prisoners to the gods if they were to win, and she orders Traxalla (who is fiercely jealous of Montezuma''s success and consequent fame and popularity) to do so. Acacis and Montezuma are talking and confess their mutual love for Oraxia, the Inca''s daughter, and rush off together to rescue her. (During the course of their conversation, it is revealed that the former king died, and his pregnant wife Amexia fled, none knew where).
The queen enters in triumph, having put Montezuma in chains--yet she falls in love with him, and is torn in her determination to execute him, but not (though from jealousy now) from her decision to sacrifice the Inca and his daughter. Traxalla gets wind of this and decides to look after his own interests (throughout the play, he shows himself to be primarily an opportunist).
Meanwhile, the queen goes to the priest, who calls up the God of Dreams to interpret a dream she had--but the god refuses. The queen then swears to burn all the gods'' temples down if they can''t (or won''t) make Montezuma burn with passion for her, Zempoalla, alone.
Traxalla brings the Inca''s daughter to Montezuma, to try to deliver Zempoalla from her passion for the young stranger. Montezuma is exceedingly contemptuous and defiant to the queen, hence Traxalla succeeds in this, and he and Zempoalla are reconciled--the queen then imprisons Montezuma and vows the sacrifices will continue. Her son Acacis, however, sets them free (he is extremely noble in attitude and actions throughout the course of the play).
Acacis comes and sends Oraxia away. Then he fights with, and is wounded by, Montezuma. Oraxia returns, and the queen and the general come back and imprison them again--her wounded son promising to sacrifice himself if the princess dies, which he does, although she lives.
In the final scene the true queen returns, and turns out to be Montezuma''s mother. Traxalla''s perfidy is punished, as the true prince stabs him to death. The people proclaim Montezuma their true ruler--all are forgiven, but the false queen, Zempoalla, takes her own life rather than live degraded from empire, with her son and her consort dead. The Inca gives his daughter to Montezuma, and order is restored.
Much of Zempoalla''s fate is self-ordained, as she says with her dying breath. She means to sacrifice the Inca and his daughter, descendants of the Sun God, and near-gods themselves. Montezuma is also acclaimed as a god himself (as the historical Montezuma was). Zempoalla lacks the nobility required for her position, a frequent fault of the usurper, though her son had this in extraordinary measure (his only fault was weakness and inability to triumph is competitive situations--a terrible fault in a ruler in times of war and conflict). Traxalla is obviously and opportunist, with nothing in view ultimately but his own interests.
While this play is historically inaccurate in some respects, it is a bold, though rarely recognized, support of the Royalist cause, and the Divine Right of Kinds, in the time of the Protectorate of Cromwell.