Act I
In their royal apartment in Trachis, Hercules’ wife Dejanira anxiously awaits his return from the war against Oechalia. Hyllus, their son, arrives with a gloomy prophecy from the Oracle predicting Hercules’ death. Dejanira fears she will never see him again on earth, but only in the shades of Elysium. But the herald Lichas arrives with comforting news: Hercules has defeated Oechalia and is about to return with a train of captives, including the Oechalian princess Iole. A march announces the arrival of Hercules, who rejoices that, having satisfied the rage of Juno, the goddess of marriage, he can now rest in peace at home. He grants Iole her freedom within Trachis, but she continues to mourn the death of her father at Hercules’ hands and her loss of liberty.

Act II
Scene 1, Iole’s apartment: Iole bewails her ruined stature. Enraged with jealousy, Dejanira enters, convinced that Hercules has been unfaithful to her with Iole. Iole firmly denies the charge, saying that Hercules ruined her land and killed her father. She warns Dejanira to beware of jealousy, which kills love and peace. After she leaves, Dejanira repeats her accusations to Lichas, who also cautions her. Having fallen in love with Iole, Hyllus appears and tries to woo her. She remains unsympathetic to such ardor, coming as it does from the son of her enemy. She urges him to not give way to the weakness of love; Hyllus, backed by the Chorus, declares the universal power of the “wanton god of amorous fires.”

Scene 2, Hercules and Dejanira’s apartment: Dejanira bitterly scolds Hercules for having been conquered by a “captive maid.” Not realizing the seriousness of her accusation, Hercules blithely dismisses it as false and departs to inspect preparations for the solemn rites at the Temple that will celebrate his victory. Left alone, Dejanira’s rage intensifies. She suddenly remembers she has a vest dipped in the blood of the dying centaur Nessus, slain by Hercules, who told her this garment would serve as a “love charm.” Hoping to regain Hercules’ love through this stratagem, she summons Lichas and commands him to take it to the Temple and urge Hercules to wear it as a “pledge of reconcilement.” Iole enters, and Dejanira apologizes for her earlier hostility, promising she will help restore her to royal power.

Act III
At the Temple of Jupiter, Lichas describes the horror of the scene after Hercules puts on Dejanira’s gift. The heat of the altar’s flames has melted the Hydra’s poison in Nessus’ blood and coursed through Hercules’ body. In agony, he tries to tear it off, but only tears away his flesh. We then see the scene ourselves as the dying Hercules curses Dejanira and begs Hyllus to carry his body to the top of Mt. Oeta and burn it on a funeral pyre, so that his immortal soul can escape to the gods of Olympus.

At the palace, Dejanira—who had unknowingly carried out Nessus’ revenge and brought about Hercules’ terrible death—has a vision of the Furies pursuing her to torment her guilty soul. When Iole enters, Dejanira tries to blame the tragedy on her, but then realizes she herself is the sole “guilty cause.” Despite her own suffering, Iole feels empathy for her captors’ plight. The Priest of Jupiter enters with the consoling news that Hercules’ soul, carried aloft by an eagle, has been accepted by the gods. He then tells Hyllus and Iole that their destiny is to marry, thus wrenching a happy ending from the tragedy. The Chorus sings in praise of Hercules as the bringer of peace and freedom.