Libretto by WS Gilbert and music by Sir Arthur Sullivan

ACT I

Princess Ida, daughter of King Gama, is due to meet Prince Hilarion, son of King Hildebrand.  They were betrothed to each other twenty years before - she was one and he, two years old.  King Hildebrand declares that if King Gama does not come before sunset, bringing the Princess with him, he will trounce them both.  Incidentally, he does not cherish his meeting with Gama,  who is twisted in body and warped in mind, his one pleasure being to wound with his spiteful tongue.  Hilarion sings a ballad in anticipation of his meeting with Ida. He is unsettled by the rumour that the Princess has forsworn the world, and formed a University for women in an old country house, Castle Adamant.

The sons of King Gama approach, and declare their strength and might.  Gama follows with a song that reveals his truly spiteful nature.  He has absolutely no insight as to why people say he is a disagreeable man.  After a bitter exchange with Hildebrand, Gama informs Hildebrand that he has not brought the Princess, who has refused to leave her female recluse.  In this retreat, having renounced mankind, even the crowing is done by an accomplished hen!

Gama indicates that if Hilarion wishes to win the Princess' hand, he would have to 'humbly beg and humbly sue'.  That said, Hilarion prepares for a mission to enter Castle Adamant with his trusty friends, Cyril and Florian.  However, Hildebrand retorts that Gama and his three sons shall remain hostage whilst the men embark on their mission.

ACT II

In Castle Adamant, the graduates of the Women's University are discovered seated at the feet of Lady Psyche, the Professor of Humanities. They are interrupted by the entry of Lady Blanche (Professor of Abstract Science), who reads out a list of crimes and punishments.  

As Princess Ida approaches, the maidens welcome their Leader as a 'Mighty maiden with a mission'.  She delivers her inaugural address, which takes the form of a tirade against Man. 

Lady Blanche lectures on Abstract Philosophy, under three guises: 'The Is, the Might Be, and the Must'.  As Lady Blanche reflects on her position after the Princess and the maidens leave, it is evident she considers herself a better Principal than the Princess.

As the luncheon bell tolls, the assembled maidens and professors gather for lunch.  The Princess hears that the three new students know the Court of King Hildebrand.  She makes sly inquiries about Hilarion.  The disguised Hilarion answers, but his appropriate eloquence and disguise is interrupted by the inebriated Cyril, who has drunk too much wine.  His 'kissing song' reveals the newcomers as men.

In a panic, the Princess, runs towards a rustic bridge in the castle grounds, misses her footing and falls into the river below.  Hilarion springs in after her and brings her safely to shore, to great applause. Ida, however, is furious and orders the arrest of the three young men, and the three are marched off.

As Lady Blanche departs, Hilarion and his two friends are seen climbing the wall.  They find some academic robes and pose as three wellborn maidens who wish to join the University - to the Princess' delight. Together they lament the hollow pleasures of the world.  Their chances of success appear high - until Lady Psyche recognises her disguised brother, Florian.  She reveals that if they are discovered, the penalty is death.  Nevertheless, she embarks on a song about the University's mission.

Meanwhile, Melissa, another of the girl graduates, enters unobserved and overhears them. Her fascination with men prompts her to keep the secret.  They sing a quintet, which contradicts the teachings of the Princess.  Lady Blanche has heard the singing and remarks on how odd it is that of the three new "girls" two should be tenors, and one a baritone.  She then discovers that a reticule dropped by one of the new 'maidens' contains not only scissors and needles, but . . . cigars!  Lady Blanche's natural instinct is to report the intruders to the Princess, but Melissa pleads with her and reminds her that if Ida were to marry, Blanche would be left to 'rule the roast.

As the men are escorted away, Melissa rushes in and informs the Princess that an armed band is without the Castle walls, demanding admittance in the name of King Hildebrand.  Almost immediately, the gate is battered down, and soldiers rush in; with them are the three sons of King Gama in chains. Hildebrand tells the Princess that he has come to claim fulfillment of the vow which was made when she was a child, and that if she refuses, he will raze her castle to the ground. The three brothers, Arac, Guron and Scynthius add their pleadings, for Hildebrand has promised them that if he fails in his quest they will most certainly be hanged.  He gives Ida 24 hours for her answer - she remains defiant.

ACT III

The Princess has decided to fight, and the ladies are assembled, armed with battleaxes. The Princess enters and issues her instructions. However, her theories meet with difficulties in practice as not one of the ladies is willing to perform the duties allotted to her. 

King Gama is summoned, and, accompanied by his three sons, he explains that Hildebrand is loth to war with women, and he has sent the Princess's brothers to fight for her against Hilarion and his two friends. Gama tells Ida of the torture he has endured during his detention by Hildebrand's, which moves Ida to yield to agree to the contest taking place. The gates are opened and soldiers with the three sons of Gama enter.

Hilarion, Florian, and Cyril are led in, still bound and robed in academic gowns. As Gama taunts them about their unusual appearance, the fight takes place.  Gama's sons, who are 'not intelligent' have rid themselves of armour, and as such, have lost in battle to Hilarion and his friends.  In defeat, the Princess seeks permission to resign her post, and asks Lady Blanche whether she will be willing to take her place.  Naturally, Lady Blanche accepts and indulges in a little abstract philosophy.  

So the Princess yields to Hilarion, Lady Psyche to Cyril, and Melissa to Florian. Lady Blanche is left, having achieved her heart's desire to be the principal of the "University." She promises the other three that they shall return to their former positions should they ever desire to do so, and the opera ends in general joy.