The story of HMS Pinafore is a classic nose-thumbing towards the monarchy and the caste system. Captain Corcoran, well-loved by his men, and extremely gentlemanly (Though bother-it I may, occasionally say, I never use a big big "D") brings his ship to harbor. There, while resupplying, Buttercup, a vendor, professes her love to him. However, despite the fact that he returns her love, he cannot wed her due to his high station of birth (only nobility could hold the position of Captain in the Royal Navy).

Sir Joseph Porter decides to do a surprise inspection of the ship and decides to marry Corcoran's daughter Josephine, while singing about how he rose from a lowly office boy at an attourney's firm to become the leader of the Queen's Navy. Ralph, a british tar and too low of a class to get Corcoran's blessing, meanwhile decides to elope with Corcoran's daughter who is in love with Ralph. Dick Deadeye rats out the couple to the Captain, who then begins to curse "Dammy!" (or "Damn Me!") at the top of his lungs.

Such conduct is unthinkable from a Captain in the Royal Navy. As such, he is relieved of duty by Sir Joseph Porter and will have to stand trial. Consequently, Ralph is also caught and is to be put to death. Buttercup thankfully comes to the rescue, and reveals that she was nursemaid for both Corcoran and Ralph, and that she accidently switched the two of them at birth. Thusly, Corcoran cannot really be a Captain, and thus can't be held accountable for cursing out loud. Ralph cannot be at fault for marrying Corcoran's daughter because Ralph is now Captain. So Corcoran marries Buttercup, Ralph marries Josephine, and Sir Joseph Porter ends up with some questionable relations with an aunt of his.

No, really, it's a good story...