I've just read THE HIDDEN PEOPLE, by Alison Littlewood, a richly textured and deeply disturbing novel about fairy changelings—maybe. We never quite find out for certain whether fairies exist, since the story is told in first person by a troubled, confused narrator. The protagonist, a young Victorian gentleman, travels to rural Yorkshire to investigate his cousin's murder by her husband on the grounds that she'd been stolen by the Hidden People and replaced by a duplicate. Although disdainful of the villagers' superstitious beliefs, the narrator gradually gets drawn in, until he begins to think his own wife might be inexplicably changing. This novel was inspired by the real-life case of Bridget Cleary, whose husband burned her to death as a suspected changeling in an Irish village in 1895. Angela Bourke's THE BURNING OF BRIDGET CLEARY tells the full story.
I've long been fascinated by the concept of changelings, probably because they embody one of my favorite themes, "fish out of water." Of course, we most often think of them as babies switched soon after birth, rather than adults. Folklore speculates that fairies take human infants because their own bloodlines have run thin so that they don't bear children very often or they give birth to sickly infants. A baby not yet christened faces particular danger and should be protected by charms and cold iron. If a child appears to have been replaced by a fairy doppelganger, a variety of "cures" can be used to force the "good folk" to take back the replacement and return the "real" child. If less drastic methods don't work, one last resort is to hold the changeling over the fire—the remedy inflicted on Bridget Cleary in real life and Lizzie in THE HIDDEN PEOPLE.
Some other recommended fiction on this topic: Maurice Sendak's haunting picture book OUTSIDE OVER THERE has the same plot premise as the movie LABYRINTH: A girl, impatient with taking care of her baby brother, wishes he would disappear. The fairies or goblins steal him, and she goes on a quest to save him. In Delia Sherman's YA novel CHANGELING (and sequels), the heroine, Neef, has grown up in "New York Between," a parallel version of the city inhabited by elves, mermaids, demons, and other mythological creatures. She knows she's a human changeling and is happy with her status—until she breaks fairy law and risks becoming a sacrifice to the Wild Hunt. Kaye, the protagonist of Holly Black's much darker TITHE (and sequels), is the opposite of Neef. Although Kaye has interacted with fairies all her life, she has no idea she's one herself, a changeling left in place of a human baby.
In pre-scientific eras, the changeling belief offered a potentially comforting explanation for babies who were born weak or deformed, looked healthy at birth but turned sickly soon afterward, refused to eat and failed to thrive, or suffered from then-unidentified conditions such as autism. If such a "changeling" reverted to "normal," the magical remedies must have worked. If the baby died, parents could cling to the belief that a changeling had died and their own child was living happily with the fairies. As for young women, who might be whisked away to the faerie realm to infuse fresh blood into the elven race, a wife who suddenly became "querulous," "unnatural," or "shrewish" could be accused of having been replaced by a changeling. An ingenious pretext for husbands intent on controlling their wives' speech and behavior!
Like witchcraft persecutions, changeling beliefs could have been used as a means of social control. Diana Gabaldon combines the two superstitions in OUTLANDER, when one of the charges in Claire's trial for witchcraft (resulting from a rival's scheme to get rid of her) accuses her of involvement in the death of an alleged changeling infant left out for the fairies to reclaim.
Margaret L. CarterCarter's Crypt