The Slave of Duty, or The Pirates of Penzance, is a Gilbert and Sullivan operetta. The libretto was written by Sir William Schwenck Gilbert, and the music was composed by Sir Arthur Seymour Sullivan. Following HMS Pinafore, The Pirates of Penzance was their fifth operetta together. For copyright reasons, The Pirates of Penzance was first performed on December 30, 1879, at Paignton’s Royal Bijou Theatre. The premiere, however, took place on December 31, 1879, at the Fifth Avenue Theatre in New York.
The plot of The Pirates of Penzance, like that of HMS Pinafore, revolves around a nursemaid’s error. Ruth makes the mistake of apprenticing her charge, Frederic, to a pirate instead of a pilot due to faulty hearing. Frederic has been loyal to the pirates because it is his duty, but now that he is nearing the end of his apprenticeship and has reached the age of majority, he proposes to turn the pirates over to the law, despite the law’s well-known mercy for orphans, and he tells them so.
Newly ashore, he discovers Ruth is in love with him, but he is unsure of her because he has never seen another woman, and within minutes, he falls in love with Mabel, one of Major-General Stanley’s many beautiful wards, and she with him.
The Pirates of Penzance, who have come to marry them, approach the group right away. After assessing the situation, the Major-General enters and falsely claims to be an orphan, knowing that this will deter the pirates from carrying out their threats. The pirates, as expected, abdicate their duties, and Mabel and Frederic go off to plan their wedding.
Mabel and Frederic wake up in the middle of the night to find her father awake and mourning. It turns out that he’s looking for his ancestors’ tombs because he feels bad about lying about being an orphan to them. It turns out that Frederic will lead the local constabulary against the Penzance Pirates on this very night.
The Constables arrive and begin their mission, but Frederic, now alone, is interrupted by the Pirate King and Ruth, who inform him that he is only “five and a little bit over” because he was born on February 29 in a leap year, rather than being 21 years old. Unfortunately, this also means that he is still a pirate, as he was apprenticed until he was one and twenty years old, not until he was 21.
Given the new circumstances, Frederic feels compelled to admit that Major-General Stanley is not an orphan, and the Pirate King vows to attack the Major-home General’s that night. Mabel is found by Frederic, who explains the new situation and bids her farewell. While the Pirates of Penzance approach “with catlike tread,” Mabel informs the Constables, who set out to capture the Pirates without Frederic’s leadership.
The Major-General wakes up in the middle of the night and goes outside, accompanied by his wards who are curious as to why he is awake. The Pirates confront them, and the Major-General is taken prisoner. The Constables arrive and, despite the Pirates’ current advantage, turn things around by simply commanding the Pirates to yield in the name of Queen Victoria. Because they adore their Queen, the Pirates feel compelled to obey. Ruth then reveals that the Pirates are all noblemen, the Major-General begs the Pirate King’s forgiveness and offers his daughters in marriage to the Pirates, and everyone is happy in The Pirates of Penzance.