1. The rocky coast of Conrwall, England
2. A moonlit ruined chapel

• Major-general Stanley, baritone
• The pirate king, bass
• Frederic, the pirate apprentice, tenor
• Sergeant of police, bass-baritone or second tenor
• Mabel, General Stanley’s most beautiful daughter, soprano
• Ruth, a pirate maid of all work, contralto

Right at the start the overture bears witness to composer Arthur Sullivan’s mastery: elegant music, skilfully and tastefully scored. The choir has lots to do and gets a chance to shine in the lovely unaccompanied 'Hail Poetry' chorus. Wonderful duets and trios, stirring finales, a breathtaking pattersong for the Major-General, coloraturas for Mabel, lyricism for Frederic, a sizeable role for contralto Ruth, all these make this work a jewel in the repertoire (especially ideal for amateur societies).

While paddling at the seaside, the Major-General’s numerous daughters are surprised by pirates. Luckily their father appears in time; he saves the girls by declaring that he is an orphan - the pirates being known never to harm orphans, as they are all orphans themselves. Mabel, the most beautiful of the Major-General’s daughters, decides to marry Frederic, a twenty-one-year old pirate. In the second act the police are to capture the pirates, led by Frederic, who has decided to give up piracy. However, the Pirate King and Ruth, his maid-of-all-work, inform Frederic that he is legally bound to piracy: his contract will expire on his twenty-first birthday, which is still a long way off because he was born on leap-day. The young man dutifully rejoins the pirates; together they vanquish the police, who, however, summon them to surrender, "in queen Victoria’s name". The pirates, who besides being orphans, are fervent royalists, immediately obey. Then the maid-of-all-work reveals a secret which enables all the ladies to marry all the gentlemen.