FROM THE 19TH-century Bildungsromane of Dickens and Twain to the delinquent diary-entries of Hinton and Salinger, writers and readers have long been attracted to the child narrator — a device that offers a level of emotional and imaginative directness unavailable to the baggage- laden adult.

Recently novelists have gone a step further, creating characters whose displacement is not only physical (like Pip or Huck), but also intellectual. Christopher, the autistic 15-year-old of The Curious Incident of the Dog in the Night-time, is a mathematical genius who cannot read emotions; Jonathan Safran Foer’s Extremely Loud and Incredibly Close is held together by Oskar, a precocious and obsessive nine-year-old polymath; the narrator of M. J. Hyland's first novel How the Light Gets In, Louise, is a highly intelligent, damaged 16-year-old, whose uncontrollable outbursts mar her chances for happiness.

In a sense, these writers are having it both ways; they can exploit the freedom and freshness of the child narrator without having to make too many compromises in vocabulary or intellect. When it works, as in How the Light Gets In, it works brilliantly — which is perhaps why Hyland has returned to it for her second novel, the disturbing and affecting Carry Me Down.

The story, set in early 1970s Ireland, is told by John Egan, an 11-year-old only child living with his parents and grandmother. Like Louise, John is different. He is too tall and his voice has already broken — other children call him Troll. He stares too long. He thinks too much. He asks too many questions. “Talking to you,” says his uncle one night, “is like watching a ventriloquist's dummy with the ventriloquist nowhere to be found.”

John wants to “make an impression in the world”; to merit an entry in his bible, The Guinness Book of World Records — but he is unsure how.

Then he discovers his “gift”: he can, with alarming accuracy, identify lies. The reaction is physical, and initially involuntary: he vomits. But as he grows to understand his ability, he learns to control it. It will, he believes, be his escape route from his mundane and misunderstood existence: he will fly to Niagara Falls, and be interviewed by his hero, Robert “Believe it or not” Ripley.

John is preternaturally perceptive, but his blind-spots are significant. As his familial relationships become increasingly fraught, the lies become more serious.

John’s grasp on emotions is sketchy: when he finds a dying cow, he has “a feeling almost like an emotion” but he doesn’t know “which kind”. His insistence on the truth regardless of the emotional context leads to the unravelling of his family and of his own delicately assembled mind.

John exists, like the narrators of The Curious Incident and Extremely Loud, in a liminal state, between adult and child, reality and fantasy, sanity and madness — but he is more unpredictable than Christopher and more enigmatic than Oskar. The resulting uncertainty gives the novel a gripping edge, but it also leads to John’s most dramatic aberration — the one moment in which Hyland’s plot-guiding presence becomes uncomfortably apparent. In the main, though, her touch is expertly light, and her creation — with his logician’s mentality, eccentric obsessions and good intentions — is instantly likeable and convincing.

In beautifully detailed and understated prose, Hyland’s meditation on the nature of falsehood uncovers precious truths at every turn.

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