I have not seen what I assume is a television adaption and would strongly recommend against anyone bothering with it as a sacrilege. This is Conrad's first and best work as it sets the narrative style ('freezing diachronic tension into a synchronic pattern') and existential dilemma (ontological insecurity) - our narrator repeatedly states that he has no self-knowledge - explored in his subsequent work. There are no females in the story. The ship has not been abandoned by its crew. The 'secret sharer' - Leggatt - is Capt. Lingard's 'doppelganger;. The question is the young captain's crisis in taking the first action of his command - an act that could result in shipwreck and the loss of his crew when he encounters Leggatt - an actual murderer - and hides him in his L-shaped cabin (divergent choice). Academics argue Conrad's intention: semiologists (from Jung) would have archetypes - materialists (from Reich) would have our (non-retrospective first person narrator) in a fugue state. Among the latter are those who would argue that Leggatt is entirely imaginary - which I dismiss as the Captain of Leggatt's vessel comes aboard in search of his fugitive first mate. Anyone interested in this fascinating and complex work should read Bruce Harkin's 'The Secret Sharer: Economical Personal Narrative' in 'Conrad's Secret Sharer and the Critics' - 1962; John P. Conger's 'Jung & Reich: the body of Shadow', and R.D. Laing's 'The Divided Self'. Let us hope that an adaptation will eventually come into competent hands.
