Hippolytus, son of King Theseus of Athens, leaves his palace at dawn to go boar-hunting. He prays to the virgin goddess Diana for success in the hunt.
His step-mother Phaedra, wife of Theseus and daughter of King Minos of Crete, soon appears in front of the palace lamenting her fate. Her husband has been gone for years after journeying to capture Persephone from the underworld. Phaedra has been left alone to care for the palace, and she finds herself pining for the forests and the hunt. Wondering what is causing her desire for the forest glades, she reflects on her mother, Pasiphaë, daughter of Apollo, who was cursed to fall in love with a bull and give birth to a monster, the Minotaur. Phaedra wonders if she is as doomed as her mother was.
Phaedra's aged nurse interjects that Phaedra should control the passions she feels, for love can be terribly destructive. Phaedra explains that she is gripped by an uncontrollable lust for Hippolytus, and that her passion has defeated her reason. Hippolytus, however, detests women in general and Phaedra in particular. Phaedra declares that she will commit suicide. The nurse begs Phaedra not to end her life and promises to help her in her love, saying: "Mine is the task to approach the savage youth and bend the cruel man's relentless will."
After the Chorus sings of the power of love, Phaedra goes into an emotional frenzy, and the nurse begs the goddess Diana to soften Hippolytus' heart and make him fall in love with Phaedra.
Hippolytus returns from hunting and, seeing Phaedra's nurse, asks her why she looks so sullen. The nurse replies that Hippolytus should "show [him]self less harsh", enjoy life, and seek the company of women. Hippolytus responds that life is most innocent and free when spent in the wild. Hippolytus adds that stepmothers "are no whit more merciful than beasts". He finds women wicked and points to Medea as an example. "Why make the crime of few the blame of all?" the nurse asks. She argues that love can often change stubborn dispositions. Still, Hippolytus maintains his steadfast hatred of womankind.
Phaedra appears, swoons and collapses. Hippolytus wakes her. When he asks why she is so miserable, she decides to confess her feelings. Phaedra subtly suggests that Hippolytus should take his father's place, as Theseus will likely never return from the underworld. Hippolytus agrees, offering to fill his father's shoes while awaiting his return. Phaedra then declares her love for Hippolytus. Aghast, he cries out that he is "guilty", for he has "stirred [his] stepmother to love". He then rails against what he perceives as Phaedra's terrible crime. He draws his sword to kill Phaedra, but upon realizing this is what she wants, he casts the weapon away and flees into the forest.
"Crime must be concealed by crime", the nurse decides, and plots with Phaedra to accuse Hippolytus of incestuous desire. Phaedra cries out to the citizens of Athens for help, and accuses Hippolytus of attacking her in lust. The Chorus interjects, praising Hippolytus' beauty but noting that beauty is subject to the wiles of time. The Chorus then condemns Phaedra's wicked scheme. It is then that Theseus appears, newly returned from the underworld.
The nurse informs Theseus that Phaedra has resolved to die and asks why, especially now that her husband has come back. The nurse explains that Phaedra will tell no one the cause of her grief. Theseus enters the palace and sees Phaedra clutching a sword, ready to slay herself. He asks her why she is in such a state, but she responds only with vague allusions to a "sin" she has committed.
Theseus orders the nurse to be bound in chains and tormented until she confesses her mistress' secret. Phaedra intervenes, telling her husband that she has been raped and that the "destroyer of [her] honor" is the one whom Theseus would least expect. She points to the sword Hippolytus left behind. Theseus, in a rage, summons his father Neptune to destroy Hippolytus. The Chorus asks the heavens why they do not reward the innocent and punish the guilty and evil. The Chorus asserts that the order of the world has become skewed: "wretched poverty dogs the pure, and the adulterer, strong in wickedness, reigns supreme."
A Messenger arrives to inform Theseus that Hippolytus is dead. Out of the ocean's depths, a monstrous bull appeared before Hippolytus' horse-drawn chariot. Hippolytus lost control of his terrified horses, and his limbs became entwined in the reins. His body was dragged through the forest, and his limbs were torn asunder. Theseus breaks into tears. Although he wished death upon his son, hearing of it causes him to despair. The Chorus proclaims that the gods most readily target mortals of wealth or power, while "the low-roofed, common home ne'er feels [Jove's] mighty blasts."
Phaedra condemns Theseus for his harshness and turns to Hippolytus' mangled corpse, crying: "Whither is thy glorious beauty fled?" She reveals that she had falsely accused Hippolytus of her own crime, falls on her sword and dies. Theseus is despondent. He orders that Hippolytus be given a proper burial. Pointing to Phaedra's corpse, he declares: "As for her, let her be buried deep in earth, and heavy ay the soil lie on her unholy head!"