At the time of the First Crusade, forces led by Goffredo (Godfrey of Bouillon) are laying siege to Jerusalem, which is under the rule of the Saracen king Argante. Aiding Goffredo is the knight Rinaldo, who is in love with Goffredo’s daughter, Almirena. Almirena and Rinaldo are taken hostage by Armida, a powerful enchantress, and Argante's ally.
Act I. The Christian camp outside the gates of Jerusalem.
Rinaldo reminds the Crusader general, Goffredo, that he promised him the hand of his daughter Almirena if Rinaldo conquers the city. Argante, the Saracen King of Jerusalem, asks Goffredo for a temporary truce. Armida arrives, summoning her furies, and tells Argante that they will only conquer the city if Rinaldo is detached from the Christian army; Armida has a plan. In a grove, Almirena and Rinaldo affirm their love, but Armida arrives to take Almirena away. When Rinaldo retaliates, the women are carried away in a black cloud and Rinaldo is devastated and alone. Goffredo enters and advises Rinaldo to consult a hermit-magician to defeat Armida. Rinaldo calls on tempests and winds to aid his flight.
Act II. On a seashore.
Rinaldo and Goffredo wonder how far they must travel to find the hermit. A boat appears on the sea, and two mermaids surround it. Rinaldo is lured into the boat by a mysterious and enchanting woman who tells him Almirena has sent her. Goffredo is left alone and decides to continue the journey to find the hermit. In Armida's enchanted palace garden, Argante makes advances toward Almirena, saying he can prove his love by breaking Armida's spell. She pleads to be left alone, but Argante takes her away for protection. Armida is pleased at Rinaldo's capture and offers him her love. When he refuses, she changes her appearance to that of Almirena. Fooled at first, he is furious when the deception is revealed, and he runs out. On Argante's arrival, Armida again changes her appearance, which only exposes his affection for Almirena. Scorned by both men, Armida vows revenge.
Act III. The hermit-magician's cave at the bottom of a mountain, with a palace above.
The hermit-magician tells Goffredo that Rinaldo and Almirena are prisoners in the palace. He warns Goffredo that it is dangerous to attempt to enter the palace and gives him a special wand to conquer Armida’s witchcraft. At the palace, Armida tries to stab Almirena and Rinaldo draws his sword to defend her. Goffredo arrives and uses his wand to transform the garden. Armida again tries to stab Almirena, but when Rinaldo attacks her, she vanishes. The three Christians are relieved, but prepare for the upcoming battle. Argante and Armida reconcile and decide to fight arm in arm in battle against the Christians. The two armies fight, and the Christians win, thanks to Rinaldo. Argante and Armida are captured and profess the Christian faith. Almirena and Rinaldo are united.
- freely adapted from multiple sources, including Wikipedia