The neighboring kingdoms of Thrace and Armenia. The lives of Zenobia and her husband Radamisto, heir to the Thracian throne, are threatened by the Armenian King Tiridate, who goes to war hoping to gain possession of Zenobia. But she is faithful to Radamisto, and Tiridate’s wife Polissena also remains devoted to her unfaithful husband. Tiridate’s military campaign is scuttled by a mutinous army commander. Tiridate realizes the folly of his ways and both couples are reunited in a celebration of married love

Polissena laments the inconstancy of her husband Tiridate. He has fallen in love with Zenobia, and has attacked the Thracian city where Zenobia, Radamisto, and King Farasmane are housed. Meanwhile, Tiridate’s military commander Tigrane is paying court to Polissena, but she rejects him. Radamisto and Farasmane are taken captive by the Armenians, and are offered their lives if they will surrender. Farasmane, Radamisto, and Zenobia will not give way, however, and are prepared to die. Tiridate gives orders for father and son to be killed, but his commander Tigrane fails to carry out the command. Radamisto and Zenobia escape. As they are crossing a plain outside the city, the exhausted Zenobia begs her husband to kill her. He cannot bring himself to do so, and she throws herself into the river. Radamisto thinks Zenobia is dead and laments her loss.

Tigrane has rescued Zenobia unhurt, and now she is in the power of Tiridate. Radamisto tries to liberate her, but Polissena comes between Tiridate and Radamisto, forestalling violence. Radamisto now resorts to a ruse, disguising himself and spreading a rumor of his own death. Tiridate is pressing his attentions on Zenobia, and offers her the crown of his kingdom. Since Radamisto is believed dead, Tiridate is not guarded, and Radamisto is able to pounce on him unexpectedly. Once again, Polissena intervenes. Radamisto is about to be executed, but Tigrane mutinies against Tiridate, which prevents the death sentence from being carried out. Farasmane is reinstated as King of Thrace, and Radamisto, happily reunited with Zenobia, refrains from taking revenge. Tiridate repents, and returns to his wife Polissena.