The story concerns Frederic, who, having celebrated his 21st birthday (or so he thinks), is to be released from his apprenticeship to a band of tenderhearted pirates. He meets Mabel, the daughter of Major-General Stanley, and the two young people fall instantly in love. Frederic finds out, however, that he was born on February 29, and so, technically, he only has a birthday each leap year. His apprenticeship indentures state that he remains apprenticed to the pirates until his 21st birthday, and so he must serve for another 63 years. Mabel agrees to wait for him faithfully, the pirates try to steer clear of the pursuing police, and Mabel’s friends keep things lively and tuneful.