Again with the room! As in her 2010 best-seller “Room,” shortlisted for the Man Booker Prize and turned into an Oscar-nominated film, Emma Donoghue has confined the action of a novel within four close walls — and again, she has populated that little universe with a sharply contrasting assortment of moral types, ranging from pure as the driven snow to nasty as can be. Unlike “Room,” “The Wonder” is historical fiction, inspired by accounts of “fasting girls” over the centuries.

Our protagonist is an English nurse named Lib Wright who has served with the already world-famous Florence Nightingale in the Crimea. Lib has been called deep into rural Ireland, an area just a few years out of devastating famine, for an unusual tour of duty. “Private nursing was always narrowing,” Donoghue writes, “and the peculiarity of this particular job had intensified the effect, shrinking her world to one small chamber.”

And in that rude chamber, located on a stinky, primitive farm in the “dead centre” of the country, lies an 11-year-old girl named Anna O’Donnell. Anna has not eaten any food in the four months since her birthday, and visitors and blessing-seekers have begun showing up from all over the world hoping for an audience with the miracle child. When a local committee is convened to manage the situation, their first step is to set up a test to prove or disprove the family’s claim. To do so, they institute a two-week period of round-the-clock surveillance, with the watch being shared by Lib and a nun named Sister Michael.

Lib is a forward-thinking woman of the mid-19th century, but her anti-Irish prejudice is strong; this is an area Irish-born Donoghue, who now lives in Canada, handles with confidence and occasional humor. Lib arrives in Ireland ready to be disgusted by its backward, sexist, superstitious culture, and she is not persuaded otherwise by what she finds. She often misunderstands what her strange hosts are saying; their hygiene and cuisine are equally crude. She is determined to unmask her patient, a spoiled miss and a “false little baggage,” chanting Catholic prayers under her breath all day. Clearly Anna is not suffering from starvation — though she doesn’t take any food or betray any hunger that Lib can see.

“From having nursed alongside a variety of women,” Donoghue writes, “Lib knew that self-mastery counted for more than almost any other talent.” Little Anna obviously has this talent, but she is also bright, curious and charming, starved as much for mental stimulation as for food. As Lib takes her for walks and gives her riddles to solve, she begins to fall in love with the girl, and her outrage at the mysterious hoax overcomes her objectivity.

Just days into the surveillance, Anna’s health takes a nose-dive, indicating that some source of nourishment has been cut off by the conditions of the experiment. Lib cannot stand by and watch the girl die. Her solution will involve a handsome, intelligent Irish Catholic journalist who has come to cover the miracle for his newspaper. William Byrne has a thing or two to teach Lib about the Irish, and about her own countrymen as well.

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The unraveling of the mystery here will bring into play another Donoghue obsession, something even creepier than superstition and ignorance. As much as we can count on her to plumb the heart of human darkness, Emma Donoghue loves a happy ending. Readers who feel the same will enjoy the blaze of romance and drama she ignites to end Lib’s Hibernian adventure.

Emma Donoghue reads from “The Wonder” on Sunday, Oct. 2, at 1 p.m. at Book Revue, 313 New York Ave., Huntington; 631-271-1442, bookrevue.com