Eurpides's Children of Herakles (Heracleidae) opens at the Temple of Zeus in Athens. Iolaus, the aged friend and nephew of Herakles and guardian of the deceased hero's younger children, supplicates the goddess Athena for protection against the wrath of Eurystheus, the king of Argos. The king seeks to murder the children, fearing that they'll take revenge on him when fully grown for his many acts of cruelty toward their father.

Suddenly, Copreus, a herald of Eurystheus, arrives, throws the old man to the ground, and seizes the children. Demophon, the king of Athens, is quickly summoned and, horrified by this treatment of Iolaus and the children, announces that he is putting them under his protection. Angered by the loss of his prey, Copreus threatens to return from Argos with an army.

When Demophon consults the oracle on how best to proceed, he receives an unwelcome augury: a maiden of noble birth must be sacrificed to the goddess Persephone in order to guarantee victory in the forthcoming battle with Eurystheus. Facing a painful dilemma and unwilling to sacrifice his own daughter to defeat an enemy, Demophon has a reluctant revelation, which rekindles the fears of Iolaus.

However, when Macaria, one of the daughters of Herakles, learns of the prophecy, she offers herself as a sacrificial victim, realizing that this will not only spare the lives of her siblings but will also prevent the death by lottery of an innocent young Athenian woman.

On the day of battle, Hyllus, a grown son of Herakles, arrives leading an auxiliary force. After Eurystheus refuses the young man's challenge to single combat, Iolaus prays to Zeus that he might, only for this day, regain the strength of his youth, to take revenge against his tormentor. His prayer answered, he defeats and captures the Argive king. Eurystheus accepts an inevitable death sentence, but his request that he be buried near the Pallenian temple of Athene is rejected by Alcmene, the sanguinary mother of Herakles. She demands that his body be thrown to the dogs, that no trace of him remain in the city of Athens.