Iolanthe used to be the life and soul of Fairyland but was banished 25 years ago for marrying a mortal. Now, pardoned by the Fairy Queen she returns as a beautiful teenager, but with a 24-year-old son, Strephon, who is half fairy, half mortal. He is in love with Phyllis, a ward of the rather susceptible Lord Chancellor. For a while, these complications wreck havoc with the proceedings of the House of Lords, giving Gilbert a chance to poke fun at that august institution.