Joseph Conrad 
The Secret Sharer [EPUB ebook] 

The story takes place at sea, near the Gulf of Siam. The young captain is unfamiliar with both his ship and his crew, having only joined their company a fortnight earlier. He soon encounters a naked swimmer holding onto the side ladder of the ship while he is alone at night on look-out duty. He helps the mysterious swimmer onto the boat and hides him in his cabin without the rest of the crew’s knowledge.