The Christian army, led by Goffredo, is besieging the city of Jerusalem. If the city is taken, then the Christian warrior Rinaldo will be free to marry Goffredo's daughter Almirena.
In an audience with Goffredo, Argante, the king of Jerusalem, is granted a three-day halt to hostilities. The sorceress Armida, queen of Damascus, descends from the skies and tells her lover Argante that their only hope of victory is the destruction of Rinaldo.
As Rinaldo and Almirena express their love for each other, Armida snatches Almirena away. Goffredo and his brother Eustazio discover the distraught Rinaldo. Eustazio suggests seeking the help of a Christian sorcerer who lives in a cave at the foot of a mountain.
Goffredo, Eustazio and Rinaldo are wandering the seashore searching for the sorcerer when a spirit lures Rinaldo on board a ship by claiming to be sent by Almirena.
In a garden of Armida's palace garden, Argante reveals his love for Almirena and offers to help her, but she repulses him.
When Rinaldo arrives, Armida's initial triumph over him turns to love, but she is rejected. Armida transforms herself into the guise of Almirena, but Rinaldo again rejects her, fleeing when he discovers her trickery.
Armida again disguises herself as Almirena, but this time Argante enters and inadvertently reveals his feeIings for Almirena. Armida is outraged and swears revenge.
Goffredo and Eustazio approach the mountain with Armida's palace at its summit and the sorcerer's cave at its foot. The sorcerer tells them that Almirena and Rinaldo are held by Armida, and the two warriors set off with two magic wands as protection.
Armida is about to stab Almirena, but Rinaldo rushes to protect her. Goffredo and Eustazio enter and with their wands transform the enchanted garden into a desert. Armida disappears. Argante attempts to rally his generals, and he and Armida are reconciled.
Battle commences, the Christians prevail and the two lovers are reunited. Argante and Armida are captured and, realizing the error of their ways, embrace the Christian faith.