Conrad, Joseph: The Secret Sharer, v.1, 18 Dec 2007.
 

A novella written in 1909, and first published in book form in 1912.

The title could also be read as ‘ Secret-Sharer’ as well as ‘Secret Sharer.’

This is the story of a young ship’s captain, early in his career, with an unfamiliar ship and crew, feeling the responsibilities of his command. Then he unexpectedly finds a Doppelganger to share his quarters and his secrets.