After Iolanthe, a fairy, committed the capital offense of marrying a mortal she has been banished from Fairyland for life. She also gave birth to the mortal's son, Strephon, who, as a result, is half mortal, half fairy. After the Queen of the Fairies, who was fond of Iolanthe, agrees to pardon her, Iolanthe announces that her son Strephon will soon be married to Phyllis, an Arcadian shepherdess. Problems occur when it turns out that every member of the House of Lords is also in love with Phyllis. The Lords and Phyllis happen upon a meeting between Strephon and his mother (who still looks seventeen) and the Lords convince Phyllis that Strephon is being unfaithful. The fairies then punish the Lords by sending Strephon to Parliament and casting a spell that makes all the peers pass any bill that Strephon wants. Phyllis soon forgives him and the two are once again in love. After the Lords complain to the fairies about Strephon's success, the fairies end up falling in love with them. In the end, the Queen of Fairies changes the law banning fairies from marrying mortals. Thus, each fairy ends up marrying a peer, while the Queen marries a Grenadier Guard, Private Willis.