Modernism
In some ways, "The Secret Sharer" looks a lot like conventional realism. But what makes it especially modernist is the way Conrad constantly plays with the line between fact and fiction. For starters, Conrad bases much of this book on personal experience but chooses to turn it into a fiction. On top of that, we're left unsure over whether Leggatt is a real person or a figment of the narrator's imagination. We'd us like to say one way or the other, but the fact that Conrad makes this question impossible to answer shows a level of experimentation that makes the book distinctly modernist.