The Pirates of Penzance; or, The Slave of Duty is a comic opera in two acts, with music by Arthur Sullivan and libretto by W. S. Gilbert. The story concerns Frederic, who, having completed his 21st year, is released from his apprenticeship to a band of tender-hearted 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 29 February, and so, technically, he only has a birthday each leap ...