the title itself serves as an example of foreshadowing; it is anallusion to an English ballad of the same name in which a scorned lover, back from the dead, comes to his ex fiance's wedding (to someone else, of course), to claim her for himself.  Readers familiar with this reference can expect, once they begin reading the story, that Mrs. Drover's ex-fiance, who was "missing, presumed dead," might return for her.  Such a reading would suggest that Bowen intended to construct a ghost story in her writing of "The Demon Lover."

Other critics, disagreeing with the ghost story interpretation, suggest that "The Demon Lover" is a psychological drama that shows the effects war can have on an already-fragile psyche.  In this case, direct characterization of Mrs. Drover tells readers that her "most normal expression was one of controlled worry."  Furthermore, we learn that Mrs. Drover, as the result of a serious illness that coincided with the birth of a child, has an "intermittent muscular flicker to the left of her mouth."  Those who view Mrs. Drover's encounter in the cab as a hallucination--the result of a psychological breakdown--might have viewed her worry and muscular flicker as signs of a nervous disorder.  In this case, Mrs. Drover's history of such signs foreshadows her breakdown at the end of the story. 

Foreshadowing is a literary technique that gives the reader some preparation or hint of what might be coming later on in the story.

Examples of foreshadowing in "The Demon Lover" start in the first paragraph, suggesting to us from the start that we are entering the realm of a ghost story. For example, we learn that "in [Mrs. Drover's] once familiar street, as in any unused channel, an unfamiliar queerness had silted up." In addition, the air in Mrs. Drover's house feels "dead."

Ghost or gothic stories revolve around the familiar becoming unfamiliar or unhomelike. At first, we might take the unfamiliarity of Mrs. Drover's house as due to the blitz: the house is boarded up and the street is deserted. Like her own family, Mrs. Drover's neighbors have escaped to the country to avoid the bombings.

However, when Mrs. Drover enters her house, she "stop[s] ... dead" as she sees a letter. The repetition of the word dead foreshadows to us that death will be a theme of this story.

More foreshadowing comes in Mrs. Drover's uneasy sensation that she is being "intruded" on and from the ominous lines in the letter from her former lover: "You may expect me, therefore, at the hour arranged."

The knowledge we receive that the lover has been missing and assumed dead since 1916 foreshadows that the encounter Mrs. Drover will have will be with a ghost of some kind.