Once upon a time there lived a fairy called Iolanthe.  She was an awfully jolly girl and leader of the Bright Young Things in Fairyland.  But, she married a mortal and that was not at all a Good Thing; not only was it definitely non-U, it was punishable by death.  Iolanthe was let off lightly and was merely banished from Fairyland for life.

The fairies all found Fairyland rather dull after Iolanthe had gone and they kept on begging the fairy queen for a reprieve, but the queen was adamant - Iolanthe had married a mortal and she must take the consequences.  One of the consequences which the queen did not know about was Iolanthe's son, Strephon.  Strephon lived in England and spent his time looking after sheep; he was also quite good on the flageolet.  He had no idea who his father was, but he knew that there had been something unusual about his parentage because he was unquestionably half fairy and half mortal (with a clear line of demarcation in the region of his waist) which was distinctly awkward on occasions.  He did not tell anyone about this though, not even his girlfriends.

By the time he was twenty-four, Strephon had fallen in love with Phyllis, who also tended sheep.  Phyllis was the sweetest girl you ever knew, but she was a ward in Chancery, which means that she might not get married before she was twenty-one unless the Lord Chancellor gave his permission.  Strephon made several applications for permission to marry Phyllis but they were all turned down.  All the House of Lords said that Phyllis was far too lovely to be wasted on a mere shepherd-boy, and the Lord Chancellor gave himself a dreadful nightmare over trying to find a solution favourable to himself.  Seeing nothing else for it, Strephon and Phyllis decided to get married without the Lord Chancellor's permission and, as it happened, the day they chose for the wedding was the very day on which the fairies at last succeeded in persuading the fairy queen to forgive Iolanthe and recall her from her exile.

Iolanthe introduced Strephon to the fairy queen, who was much taken with him and even offered him a seat in Parliament.  Iolanthe was delighted at being re-united with her son and they went about a lot together.  This was Strephon's undoing, for nobody would believe that his pretty companion was his mother - she looked far too young.  Certainly Phyllis could not swallow the story and after some hard words she gave Strephon back his ring.  On the rebound she decided to marry into the peerage and soon found herself engaged to two noble lords, both at once.

In despair, Strephon invoked the aid of the fairy queen and she made him win the next Parliamentary bye-election.  He rapidly became famous in the House of Commons because every motion he supported was carried, by both parties.  His support for a Bill to open the House of Lords to competitive examination put the cat among the pigeons.

At last Strephon found a chance to explain to Phyllis about his mother and they became engaged again.  Iolanthe was deputed to tackle the Lord Chancellor, which she did with success (and a bit of shock treatment); the Lord Chancellor suggested a neat way of amending the fairy law about marriage to mortals, so the fairies married the peers and they all live happily ever afterwards.