The Pirates of Penzance, or The Slave of Duty is an operetta by Gilbert and Sullivan. Sir William Schwenck Gilbert wrote the libretto, and Sir Arthur Seymour Sullivan composed the music. The Pirates of Penzance was their fifth operetta together, following after HMS Pinafore. The Pirates of Penzance was first performed at Paignton, at the Royal Bijou Theatre on 30 December 1879 for copyright reasons. The premiere, however, was in New York at the Fifth Avenue Theatre on 31 December 1879.
The plot of The Pirates of Penzance, like the plot of HMS Pinafore hinges, on a nursemaid’s mistake. Due to faulty hearing, Ruth makes the mistake of apprenticing her charge, Frederic to a pirate instead of a pilot. Frederic has been true to the pirates because it is his duty, but now that he is about to be done with his apprenticeship upon coming of age, he proposes to hand the over to the law, despite their well-known mercy to orphans, and—honest fellow that he is — he tells them so.
Newly ashore, he finds that Ruth is in love with him, but he is not sure of her, never having seen another woman, and within a few minutes, he falls in love with Mabel, one of the many beautiful wards in chancery of Major-General Stanley, and she with him.
The group is immediately accosted by the Pirates of Penzance, who have come to marry them. The Major-General enters, and upon understanding the situation, falsely claims to be an orphan, knowing that this will deter the pirates from carrying out their threats. The pirates — true to form — desist, and Mabel and Frederic go off to plan their wedding.
Act II opens with Mabel and Frederic discovering her father awake and mourning in the middle of the night. It turns out that he has sought out the tombs of his ancestors because he feels guilty towards them for having lied about being an orphan. It turns out that this is the very night that Frederic will lead the local constabulary against the Pirates of Penzance.
The Constables arrive and set about their mission, but Frederic, now alone, is interrupted by the Pirate King and Ruth, who give him some unexpected news: since he was born on February 29 in a leap year, rather than being now 21, and of age, is is only “five and a little bit over.” Unfortunately, this also means that he is still a pirate, as he was apprenticed not until he was 21 years old, but until he reached his one and twentieth birthday.
Given this new state of affairs, Frederic feels duty bound to admit that Major-General Stanley is not an orphan, and the Pirate King vows to attack the Major-General’s home that very night. Frederic finds Mabel to explain the new situation and say farewell. Mabel passes the news on to the Constables, and the set out to capture the Pirates without Frederic’s leadership, while the Pirates of Penzance approach “with catlike tread.”
The Major-General wakes in the night and goes outside, followed by his wards who want to see why is awake. They are confronted by the Pirates, who take the Major-General prisoner. The Constables arrive, and while noting the Pirates current advantage, turn things on their heads, by simply commanding the Pirates to yield in Queen Victoria’s name. The Pirates feel obliged to obey because they love their Queen. Ruth then reveals that the Pirates are actually all noblemen, the Major-General begs the Pirate King’s pardon, and offers his daughters to the Pirates in marriage, and The Pirates of Penzance ends happily for all.
