Her Majesty’s Ship PINAFORE lies at anchor in Portsmouth harbour. On the quarterdeck the crew enthuse over their life on the ocean wave as they set about their daily routine. Their work is interrupted by the arrival of Mrs. Cripps, a local bumboat woman, come to sell whatever she can from her basketful of treats and little luxuries. Known affectionately by the men as Little Buttercup – though she could never tell why – she is struck by the melancholy appearance of one of the sailors. His name, she learns, is Ralph Rackstraw - a revelation that clearly troubles Buttercup. Ralph is passionately in love, but with a lady so far above his social station that he regards his suit as hopeless. This lofty lady is well known to his crewmates, for she is none other than Josephine, daughter of their own ship’s commanding officer, Captain Corcoran.

The Captain appears on the deck and exchanges compliments with his crew. He is certainly a popular commander who, before his men, gives every indication of confidence and stability. Yet when the sailors depart he reveals to Buttercup that he his deeply troubled.

His daughter is being sought in marriage by Sir Joseph Porter, the First Lord of the Admiralty; but, for some reason, she does not seem to take kindly to the match. After Buttercup’s departure Josephine arrives and admits her reluctance to be courted by Sir Joseph. The reason is simple enough: she is in love with someone else. Because the object of her affection is but a lowly sailor on board the PINAFORE, however, she assures her shocked father that she will never pursue a liaison with one so ignobly born.

Sir Joseph Porter arrives on board attended by his cousin Hebe and an entourage of adoring sisters, cousins and aunts. Proud of his rise from humble office boy to his present exalted position, he relates the stages in his progress. He then proceeds to inspect the ship’s company but finds the Captain’s manner in delivering orders to the men somewhat discourteous. After all, they are, as Sir Joseph says, any man’s equal – excepting his.

Sir Joseph’s egalitarian views endear him to the sailors who sing the glee that he has specially composed for the edification of the lower ranks of the Royal Navy. After the crew depart Josephine comes on deck. She meets Ralph, who has resolved to declare his feelings. Although she loves him, she forces herself into a show of outrage and disdain. Distracted, Ralph sees suicide as his only course and conveys his resolution to his ship-mates and the visiting ladies. Appalled, they stand back as he raises a pistol to his head. Suddenly Josephine bursts on deck. She cannot stand by and let this happen and so declares her love to Ralph. Given the obstacles to their union, elopement seems the only course and plans are hatched for a flight that very night. There is only one dissenting voice. Dick Deadeye, hated by all the crew, warns against this folly. But no-one is in any mood for his misanthropic utterances and the high spirits soon return.

Synopsis - Act Two

Captain Corcoran, alone on deck, soliloquizes to the moon about his troubles. Buttercup overhears and offers a sympathetic ear. Clearly she is very fond of the Captain, but despite his own reciprocal feelings, differences in their respective social positions, he says, make anything more than friendship out of the question. In response, Buttercup prophesises a change in store for the Captain, for with gypsy blood in her veins se can read destinies. He must be prepared – for things are seldom what they seem.

Sir Joseph, meanwhile, has been pressing his suit upon Josephine - without success. Corcoran, anxious to placate the First Lord, suggests that his daughter may be dazzled by her suitor’s exalted position. He suggests that Sir Joseph might fare batter if he were to assure the young lady that in the Admiralty it is a standing rule that love levels all ranks. The two men retire as Josephine appears. Alone, she expresses her misgivings at the irrevocable step she is about to take. Then Sir Joseph joins her and, acting on Corcoran’s suggestion, states his belief that love is a platform upon which all ranks can meet.

This statement removes all Josephine’s misgivings regarding her elopement. Sir Joseph, however, unaware of how eloquently he has pleaded his rival’s cause, thinks her positive response a sure sign in his favour. The Captain is extremely pleased at the prospect of realising his fond hope of a marriage between his daughter and a cabinet minister. His elation is to be short-lived, however, for Dick Deadeye appears soon after to reveal the plans for the impending elopement.

The Captain lies in wait, but not for long: the lovers, assisted by the crew and Buttercup, shortly appear on deck. They are about to leave the ship when the Captain step out from hiding to challenge them. He is so incensed by Ralph’s presumption that he cannot control his tongue. “Why damme, it’s too bad!”, he exclaims just as Sir Joseph and his relations arrive to investigate the commotion. They are horrified by the bad language. The First Lord dismisses the Captain, in disgrace, to his cabin, and when, in turn, he discovers Ralph’s involvement with Josephine, the young sailor is likewise ordered away.

The dramatic turn in events prompts Buttercup to speak and admit to a deed that has long troubled her conscience. When she was young she had been foster-mother to two boys, one of lowly birth and the other “upper crust”. Somehow she mixed the children up and, until now, had never admitted this terrible error. Events, however, now made it imperative that the truth be known: the well-born baby was Ralph; the Captain was the other. Amazed by this news, Sir Joseph calls for Ralph and Corcoran to be brought before him; and so they appear, Ralph dressed in a Captain’s uniform and Corcoran in the uniform of an able seaman. With the social tables turned, Sir Joseph loses all interest in a marriage with Josephine, now no more than a humble seaman’s daughter; instead he resigns himself to a union with the ever attentive Hebe. For Ralph and Josephine the reversal removes all obstacles – and so it does for Able Seaman Corcoran and his dear Little Buttercup.