This masque in classical verse is a paean to the power and rewards of virtue in the face of temptation. Jove sends an attendant Spirit to defend three noble siblings lost in a wild wood after darkness has fallen. The Spirit favorably contrasts the "starry threshold of Jove's court" with the snares of earthly life. It relates how Bacchus and the witch Circe gave birth to a son, Comus, who surpasses his mother in the black arts. He entices mortals to drink of his cup promising sensual pleasure, but they are transformed into beast-headed people who forget their former lives and, unaware of their animal countenances, think themselves more attractive than before.

Comus appears leading his monstrous band of revelers and praises the night that provides cover for their sensual pleasures. He hears the lost Lady coming and transforms himself into a shepherd to more easily ensnare her. She has overheard their revels and is wary. She trusts that a virtuous mind and her chastity will protect her, and that the "Supreme good" would "send a glistering Guardian if need were." She sings a song to the nymph Echo to attract her lost brothers' attention if they are in earshot.

Comus detects something divine in her song and compares it to the singing of the Sirens. They meet and converse. The Lady explains her predicament and Comus, in disguise, offers to help but only as a ruse to gain her trust so he can try to ensnare and corrupt her. She trusts him and follows. Meanwhile, the brothers are worried about their lost sister, but the elder brother tells the younger that their sister's virtue will protect her. The younger brother doubts, but the elder urges hope and that their sister has a hidden strength in chastity that evil cannot overpower. They encounter the attendant Spirit in the guise of their royal father's shepherd. He tells them of Comus and that the sorcerer has already captured their sister. The elder brother says he'll make Comus return his sister or slay him, but the Spirit warns him that the magician can easily "unthred" his "joynts" with his wand. The Spirit in disguise tells them he has a potent herb that can protect all of them.

In his stately palace Comus tries to persuade the Lady to drink of his glass and experience sensual pleasure. He threatens to turn her to marble with his wand if she declines but she replies she will still have control of her mind. Comus argues that nature gave her fine limbs to put to good use. She relates his previous deceptions and rebukes him. He regales her with a speech about how nature bestows beauty for a purpose, not to have it hidden and neglected. She rebukes him again with such a powerful speech that Comus is unsettled but recovers his nerve and persists.

The brothers and the Spirit in disguise burst onto the scene and repel Comus and his enchanted monsters but need help to free the Lady from his spell. They call on the water Nymph Sabrina who is a protectress of virtue. Sabrina appears and the Spirit requests she release the chaste lady from the enchantment that holds her in the sorcerer's chair. Sabrina complies and leaves and the Spirit praises her. The Spirit then urges them to leave the cursed palace and return to their father's castle.

Back in Ludlow Castle (where the Mask was first performed in 1634) dancers accompany the Spirit, the Lady, and her two brothers. The Spirit signals the end of the play, and the children are presented to their father and mother and praised for their victory over "sensual Folly and Intemperance". The dances end and the Spirit closes with a poetic eulogy to many of the classical divinities of the eternal realm and urges that mortals should follow virtue if they would rise, and that heaven itself bends down to help the virtuous when virtue is endangered.

The Attendant Spirit comes into a wild wood, far from his usual abode outside Jove’s court, far above the dirt and hubbub of the world. He is on earth only to show the rare mortals before him some of the ways to godly virtue. He speaks of the plight of three children who are traveling to visit their father Neptune, ruler of many island kingdoms. Their path lies through a dark and treacherous wood where their lives would have been in danger if Jove had not sent the Spirit to protect them. The chief danger is Comus, son of Bacchus and Circe. He lives in the wood and possesses a magic wine that, when drunk by thirsty travelers, gives them the heads and inclinations of wild animals. The Spirit disguises himself as a shepherd to guide the children of Neptune. He leaves when he hears Comus and his band of bewitched travelers approaching.

Comus, invoking joy and feasting, drinking and dancing, declares that the night is made for love and should be so used before the sun reveals the revels of his band and turns them to sinfulness. His followers dance until he stops them, sensing the approach of a young woman whom he immediately wishes to enchant.

The Lady enters, drawn to the scene by the noise of the revelers. Unwilling as she is to meet such people, she nevertheless believes that they are the only hope she has of finding her way out of the wood. Because she is tired by her walking, her brothers leave her to find wild fruit for refreshment, but night falls before they can return and they are unable to find her again. Meanwhile, a dark cloud covers the stars. The Lady calls and sings to the nymph, Echo, to guide her to her brothers.

Comus, delighted with the song she sings, decides that the Lady should be his queen, and, in the disguise of a village boy, he greets her as a goddess. The Lady reproves him and says that she wants help to find her companions. After questioning her about them, he says that he saw two such young men gathering fruit and that it will be a delight to help her find them. Comus adds that he knows the woods perfectly and that he will therefore lead the Lady to her brothers. She replies that she will trust him. They leave the clearing together.

The two brothers arrive and the elder calls to heaven for the moon and stars, so that they might see their way. Failing this, he wishes to see the lights of someone’s cottage. The Second Brother, adding that even the sound of penned-up flocks will help them, expresses great fear for his sister’s fate. The Elder Brother insists that the Lady’s perfect virtue will protect her. The Second Brother says that beauty such as hers needs to be guarded and that she can easily be in danger in such a place. The Elder Brother repeats that he has great hope for her safety as she is armed by chastity. Nothing can violate this; the very angels in heaven will protect her.

Hearing someone approaching, the brothers call out to him. When the Attendant Spirit greets them, they think they recognize him as their father’s shepherd, Thyrsis. He anxiously asks where their sister is and, hearing that she is lost, tells them that Comus dwells in the wood. He adds that he overheard Comus offer to escort a lady to her companions. Fearing that she is their sister, he leaves to find the brothers. That news plunges the Second Brother into complete despair. The Elder Brother, maintaining that virtue can be attacked but not injured, declares that they must find Comus and fight him for their sister, but the Attendant Spirit warns them that swords will not help them against Comus. He says, however, that he was given a magic herb that is effective against all enchantments. He instructs the brothers to break the glass in Comus’s hand when they find him and to seize his wand.

In Comus’s palace, meanwhile, the Lady refuses his wine and attempts to leave, but she is restrained by a threat to transfix her in her chair. When she declares that Comus cannot control her mind, he propounds his hedonistic philosophy, saying that she should enjoy her youth and beauty, not cruelly deny them. She replies that she will never accept anything from him, since only the good man can give good things. Comus argues that in rejecting him she is denying life and the plentiful gifts of nature by her abstinence; beauty should be enjoyed, not left to wither like a dying rose. The Lady decides that she must refute these arguments with her own. She states that nature’s gifts are for the temperate to use well and that excess of luxury breeds only ingratitude in men. She fears that Comus can never understand this doctrine, and she believes that if she attempts to explain, her conviction will be so strong that his palace will tumble around him. Comus is impressed by her argument, which seems to him inspired by Jove himself, yet he determines to try again to persuade her. As he begins to speak, the brothers rush in, break his glass on the ground, and overwhelm his followers.

Comus escapes because they have not captured his wand. The Attendant Spirit despairs of freeing the Lady until he remembers that he can summon Sabrina. This river nymph will help them, since she loves the virtue that the Lady personifies. By song, he summons her in the name of Neptune and Triton to save the girl. As Sabrina rises from the river, she sings of the willows and flowers that she left. She frees the Lady by sprinkling on her the pure and precious water from her fountain. The Attendant Spirit gives Sabrina his blessing and prays that the river should always flow in good measure and that its banks will be fertile.

The Attendant Spirit then tells the Lady that he will lead them to Neptune’s house, where many friends are gathered to congratulate him. In Ludlow Town, at the castle, country dancers lead the Lady and her two brothers before the Earl and the Countess, who impersonate Neptune and his Queen. There the Attendant Spirit praises the young people’s beauty, patience, and honesty, and their triumph over folly; then he announces his return to his natural home in the Gardens of Hesperus, for his task is done. If any mortal would go with him, however, his way is the path of virtue.