"The Secret Sharer" takes place on a sailing ship in the Gulf of Siam (now the Gulf of Thailand), at the start of a voyage with cargo for Britain. The date is probably in the 1880s, when Conrad was at sea himself. In common with many of Conrad's stories, it is narrated in the first person. The narrator is the ship's young captain, whose name is never given. He is unfamiliar with both his ship and his crew, having joined the ship only a fortnight earlier, and unsure of his ability to exert his authority over the officers and crew who have been together for some time. He makes the point several times that he is the "stranger" on board. After being towed downriver (presumably from Bangkok) by a steam tug, the ship is left at anchor near a group of small barren islands a few miles off shore, waiting for wind to begin its voyage. An incoming ship is anchored similarly a couple of miles away, awaiting a tug to go upriver.