Upon an initial reading, "The Secret Sharer" seems to be an old-fashioned tale of adventure on the sea. The story features a captain, his crew, a mysterious event, a murder, a near-disaster, and the saving of a ship. While "The Secret Sharer" is an adventure yarn, it also stands as a profound and often disquieting examination of every person's dual nature and how each person must resolve this duality for the self to grow. Conrad's use of the doppelganger theme — a character's double or alter-ego — allows him to explore the dual nature of his protagonist, a young yet unsure captain assuming his first command.
"The Secret Sharer" concerns a young captain who assumes the command of his ship only a fortnight before the action of the story begins. Because of this, he is doubtful, untried, and feels himself at the mercy of a crew that while not mutinous or even hostile, slightly undermines the authority that a captain should possess if he is to truly command a ship as he sees fit. Like the skipper of the Sephora (the ship from which Leggatt escaped), the Captain worries over his reputation and the means by which he can preserve it during his first command. Because he lacks the courage and conviction needed to command a ship successfully, he stands as a well-meaning yet weak example of a typical captain. Once Leggatt appears from the depths of the sea — a possible symbol of the Captain's unconscious desire to remedy his own weaknesses — the Captain's personality begins to change.
His discovery of Leggatt changes the Captain in both obvious and subtle ways. Leggatt is, by definition, a killer who murdered an insolent sailor while simultaneously saving the Sephora during a terrible storm. While Leggatt did not intentionally kill the seaman, he is still a powerful and slightly sinister figure. Thus, Leggatt (a renegade from the law) represents the more brutal, irrational side of man, while the Captain represents the more civilized and refined one. Although the Captain thinks that a ship should be run in an orderly and straightforward fashion, Leggatt struck the insolent seaman because he would not assist him in repairing a sail. This is hardly an orderly action to take, but Leggatt felt no regard for rules and regulations when the lives of his fellow sailors were at stake during the storm, and the insolent seaman refused to cooperate in repairing the sail. The Captain, therefore, represents the more rational but timid side of humankind, while Leggatt represents the more irrational but brave side. Together, the Captain and Leggatt make up a perfect commander, and Conrad's story tracks how Leggatt influences the Captain and by doing so, transforms him into the perfect commander.
Conrad's use of the doppelganger theme invites the reader to consider his or her own duality, and to struggle for a balance between the rational and irrational, the timid and bold, the public and private sides of his or her personality. According to "The Secret Sharer," one's personality is created through interacting with others who offer a glimpse into the part of oneself that one assumes he or she lacks, only to discover that it has been lying dormant, waiting to be released.
