More commonly, though, she reaches further back into the historical archive for inspiration, breathing imaginative life into biographical footnotes – a 19th-century American murder in Frog Music, a scandalous Victorian British divorce in The Sealed Letter – to create novels and short stories that are refreshingly revisionist about class, gender and sexuality.

Her new book is based on the many cases of “fasting girls” reported across the world from the 16th to the 20th centuries: women and girls, often prepubescent, who claimed to live without food for months or even years. Whether it was anorexia, religious mania or entrepreneurial spirit that was driving them, they drew donations from curious visitors and fascination from doctors, scientists and priests, keen to discover if they could really be living on air, light or the love of God. (The phenomenon divides along gender lines: while women withdrew into bedrooms that became shrines, their male equivalents, the “hunger artists” immortalised in Kafka’s story, presented starvation as a performative feat of endurance in travelling fairs, a trend culminating in illusionist David Blaine’s 44-day fast in a glass box dangled over the Thames.)

Several of the fasting girls were placed under medical surveillance, with predictable results – which is where Donoghue comes in. Lib Wright is an English nurse who has served in the Crimea under the redoubtable “Miss N”, and now takes on a well-paid but perplexing commission in an Irish backwater: to watch for a fortnight over 11-year-old Anna O’Donnell, who apparently has not eaten for four months, and thus reveal whether she is a miracle or a fraud.

Lib is briskly impatient with the heady mixture of religiosity and folklore permeating the village like peat smoke, and at first with the obliging yet resistant Anna herself. She notes Anna’s symptoms – downy cheeks, scaly skin, blue fingertips, swollen lower limbs – checks over the tumbledown cabin for caches of food, limits Anna’s contact with her parents to a brief embrace morning and evening, and expects that she will have the mystery solved in short order.

But as the days pass, no secret feeding is discovered. Anna’s condition worsens and Lib begins to wonder: “Could the Watch be having the perverse effect of turning the O’Donnells’ lie to truth?”

Donoghue draws out the narrative suspense with her customary combination of historical verve and emotional delicacy, as the mystery becomes not so much what is happening beneath Lib’s nose, but why. “Every body was a repository of secrets,” Lib muses, as she starts to look beyond her desire to expose trickery towards a truth that can be expressed only through suffering, not words. Faith, or what Lib calls “religious mumbo-jumbo”, can trump reason. Anna is mourning a dead brother, obsessively totting up how many prayers will get him into heaven, and the dark days of the famine still hang over the village. “A child now 11 must have been born into hunger. Weaned on it, reared on it … every thrifty inch of Anna’s body had learned to make do with less.” Caught at the nexus of family secrets, religious hysteria and medical hypothesis, with one doctor idly wondering if her chilled extremities are a sign that she is changing into “more of a reptilian than a mammalian nature”, Anna has only one power available to her: the anorexic’s power of refusal.

Like Room, this is a thrilling domestic psychodrama that draws its power from quotidian detail as well as gothic horror, as a woman and a child at close quarters must draw on inner resources to survive an impossible situation.

But Donoghue also sets Anna and Lib’s relationship in a wider context: of English and Irish antagonism, of the birth of nursing, of the clash between science and faith. By the end of the book, the fiercely atheist Lib has adopted Anna’s religious cadences, presenting herself as both tempter and priest. Should Anna break her fast, it will be a new kind of sacrament, an admission of the body and “such need, such desire, risk and regret, all the unhallowed mess of life”.