wenty-five years ago, the fairy Iolanthe married a mortal, thus incurring the death penalty under Fairy law. On condition that Iolanthe left her husband, never to see him again, the Queen of the Fairies commuted her sentence, sending Iolanthe instead into life-long exile at the bottom of a well.

Her son, Strephon, born shortly after her banishment, is only half a fairy and has fallen in love with Phyllis, a Ward of the Court of Chancery. As the Opera opens, the fairies persuade their Queen to pardon Iolanthe, and she returns to her son. When Strephon announces that he wishes to marry Phyllis, despite the Lord Chancellor's refusal, the Queen decides to help.

The House of Lords are enamoured with Phyllis and appeal to the Lord Chancellor to give her to whichever one of them she chooses. When Phyllis announces that she intends to marry Strephon, a mere shepherd, the Peers are outraged and separate the two of them.

Fairies, of course, never grow old, and so when Phyllis later catches Strephon caressing the young-looking Iolanthe, she cannot believe Iolanthe is really his mother. The Peers, together with the Lord Chancellor, also witness this apparent infidelity, gleefully encourage Phyllis to denounce her lover. Strephon, in despair, calls on the Queen of the Fairies to come to his aid. Phyllis, in her distress, rashly offers herself to her two most persistent lovers, Mountararat and Tolloller; she does not care which. The Fairy Queen prepares a deadly retribution.

She decrees that Strephon shall enter Parliament. He is returned by a huge majority as a Liberal Conservative and is made leader of both parties, in which position he carries every conceivable measure, much to the discomfiture of the noble Peers. As the Fairies watch over their young protege in the House, they find themselves growing attracted to the Peers. The Fairy Queen herself falls victim to the charms of Private Willis who is on sentry duty at the Palace Yard.

Will Strephon win back the devotion of Phyllis, or will she fling herself into the aged arms of her aristocratic suitors? Will Iolanthe risk a sentence of death to help her beloved son? How will the Queen balance the Fairy laws with her own romantic yearnings? Perhaps the Lord Chancellor has the answer after all...