Who is the letter from in the demon lover?

In "The Demon Lover" by Elizabeth Bowen, the letter is from a character named "K." It is addressed to the protagonist, Mrs. Drover, and it evokes memories of a past romantic relationship. The letter's unsettling content and its mysterious sender contribute to the story's themes of nostalgia, trauma, and the haunting effects of war. The ambiguity surrounding the identity of "K" heightens the tension and sense of dread throughout the narrative.