Kay and Thea are half-sisters, separated in age by almost twenty years, but deeply attached. When their stern father dies, Thea returns to Nova Scotia for her long-promised marriage to the captain of the Morning Light. But she cannot abandon her orphaned young sister, so Kay too embarks on a life-changing voyage to the other side of the world. At the heart of "The Difference" is a crystallizing moment in Micronesia: Thea, still mourning a miscarriage, forms a bond with a young boy from a remote island and takes him on board as her own son. Over time, the repercussions of this act force Kay, who considers the boy her brother, to examine her own assumptions--which are increasingly at odds with those of society around her--about what is forgivable and what is right.