The theme of appearance versus reality plays a vital role in “The Demon Lover.” Mrs. Drover is bewildered by the sudden appearance of the letter. How did it get onto the table? Who delivered it? Her home appears deserted and undisturbed, making the presence of the letter all the more puzzling. In an attempt to reassure herself of what is real, Mrs. Drover gazes into the mirror and sees her own familiar and comforting reflection.

The letter suggests that the soldier-lover plans to honor his promise made twenty-five years ago to return and "be with" Mrs. Drover. Could he be the demonic lover, returning to claim her life because she did not wait for him? This, along with the driver's relentless speeding, may imply a desire for vengeance.

Her thoughts flash back to the mysterious, nameless soldier-lover she was infatuated with in her youth. This recollection reinforces the idea of him as the potential "demon lover" referred to in the title. She remembers him not with affection, but for his control over her. Mrs. Drover’s connection of the letter to the soldier-lover casts doubt on its authenticity, even though it is a real object. When she escapes into a taxi, she sees the driver's face, causing her to scream and bang on the glass between them. What does she actually see? Bowen skillfully manipulates both Mrs. Drover’s and the readers' perceptions.

In the narrative, Mrs. Drover is portrayed as compliant, adhering to conventional female roles. She passively responds when her soldier-lover injures her hand and adjusts to him during their encounters. She permits William Drover to marry her because his courtship makes her feel “relieved.” Additionally, she is anxious and easily unsettled by the weather, the chiming clock, and the mood of the house.

Mrs. Drover is an unwitting casualty of both World Wars. She mourns the loss of her soldier-lover in the first conflict and is compelled to abandon her home for the countryside during the second. Her food supply is restricted, and her house has been damaged by bombings. Overwhelmed by the war, she clings to the hope of safely returning to the countryside with her family. Additionally, she feels oppressed by the memory of her soldier-lover, who maintains a hold over her, altering her demeanor in the eyes of her family when he is present. This influence leads her to suspect he might have been the one to write the letter.

Mrs. Drover perceives herself largely through the perspective of her family. While they consider her to be a strong and confident woman, she has buried certain aspects of her past deep in her memory. For example, she recalls her feelings for her soldier-lover and the loneliness she experienced when she vowed to wait for him. Curiously, she is apprehensive about the letter signed with just her initial, “K.” Throughout the story, she struggles to recall her soldier-lover’s appearance, and it remains ambiguous whether she recognizes him when she sees the taxi driver's face at the end of the story.

England is once again engulfed in war, profoundly affecting Mrs. Drover's life. She reflects on the soldier she knew during World War I. Interestingly, the letter she receives mentions "the fact that nothing has changed." The soldier symbolizes war and is associated with death, which haunts Mrs. Drover’s mind. On the other hand, Bowen provides a logical explanation for the letter's appearance: a change in the air as someone left the basement. Is it the war itself that makes Mrs. Drover scream while being driven through the deserted streets? This question remains unanswered, as Bowen deliberately leaves it open to the reader’s interpretation.