In 1932, towards the end of April, the Cunard liner Berengaria brought to New York an elderly English widow named Alice Hargreaves. Though she had said she was daunted by what lay ahead, the Americans she was due to meet were wildly excited, since Mrs Hargreaves had once been the creature of their dreams. A few days before embarking she had taken tea at Buckingham Palace with the young Princess Elizabeth, and had presented her with a first edition of Alice's Adventures in Wonderland. "From the original Alice," she had written in the flyleaf. That was the clue. Hers was the story that all Manhattan now wanted told.

But it was not to be. Alice, so famously née Liddell and now 80 years old, struck New Yorkers that springtime mostly as a somewhat bewildered and puzzlingly unhappy old woman. They had so wanted her to be otherwise, to lift their Depression spirits. In their hundreds they had gathered outside the Waldorf-Astoria to glimpse what they supposed might remind them of the 10-year-old child, the Alice of those golden summer afternoons in Oxford, when Charles Dodgson  the centenary of whose birth was being celebrated  had rowed her along the Thames and told her such strangely wonderful stories. That she had now become querulous and grumpy was both a public disappointment and a profound mystery. What had happened, everybody was suddenly asking. They have been asking the same question, under many guises, ever since.

With After Such Kindness Gaynor Arnold now offers some kind of answer. She is well placed to do so: a newly successful historical novelist (Girl in a Blue Dress, inspired by the relationship between Charles Dickens and his wife, made the Booker longlist), she knows Oxford well, and knows the ways and fears of children from her four decades as a Birmingham social worker. She has pursued the central mystery tangentially and allusively in a clever, skilfully woven, teasing and compelling story "inspired by Lewis Carroll and Alice". Alice is here named Daisy, the youngest daughter of the Rev Daniel and Mrs Evelina Baxter; and the stuttering photographer-don is the initially somewhat more impious Rev John Jameson. Names aside, however, all here is familiar territory.

Yet this is by no means a fictionalised forensic examination of the specific question that all want answered: did Dodgson do anything improper during the months he spent with the sprite-like daughter of the college dean, beyond photographing her on one occasion with her left nipple exposed? Certainly nothing of the kind occurs in this story between Johnson and young Daisy  except that (to the disapproving shock of her eventual husband) he does persuade her to allow him to take photographs of her naked. Everything is otherwise decorous, courteous, refined  and yes, kept guiltily secret. The girl's later troubles have their origins elsewhere. In dealing with the central question, Arnold offers an alternative and surprising scenario that manages to be both entirely plausible and psychologically fascinating. It is a scenario that triggers a cascade of events which would surely scar any child who survived it.

This pivotal moment is supremely well concocted, although the literary device used to take us around it is more than a little jarring on the page: our now-familiar Daisy, on waking one morning after the dreadful turn of events, suddenly abandons her childhood and becomes a grown-up with a brand-new name  Margaret. And Margaret, when furtively reading her own diaries years later, finds her metamorphosis quite inexplicable: "If only I could remember ," she wails, "what happened in those four years between the ages of eleven and fifteen that are such a mystery to me."

Could some psychosexual trauma, as well as distancing her from her husband, have caused her somehow to "lose" four years of her life? The way Arnold answers this beguiling question is key: for the moment that the bewildered youngster apprehends her altered looks, her fuller figure, her height, her clutch of barely suppressed memories and the curious menagerie of her dreams, everything swiftly falls into place. It is, of course, the Alice narrative, underpinning this crucial moment in the book. For in the wake of her unendurable trauma, Daisy has metaphorically swigged from the bottle marked "Drink Me" and been transported into adulthood in an instant  with an adult understanding of what has taken place.

In this thoughtful novel Margaret Baxter never goes to America, but to a psychiatrist instead. Had she gone, Americans might well have found her puzzling. The alienist here just finds her fascinating. "She might enjoy a modicum of celebrity in the annals of medical science," he writes to a colleague.

Quite so. As well might John Jameson, or Charles Dodgson, or Lewis Carroll. Or the Rev Daniel Baxter, indeed. Or even Dean Liddell. Everyone in the story of Alice, fact or fiction, will inevitably have to submit to the spotlight, time and again, for as long as Wonderland endures.

 Simon Winchester's The Alice Behind Wonderland is published by OUP.