WHEN WE WERE ROMANS

Matthew Kneale (Picador, £16.99)

Kneale's most successful novel, English Passengers, was written in the Bodleian Library while he lived in Oxford - a tour de force following dozens of different characters from England to Tasmania and back to the Isle of Man, involving Victorian theology and arcane maritime traditions, with dialogue in the pidgin language of the Aborigines and the Manx of the 19th-century sailors.

His latest book has a more limited geography, covering a journey from Britain to Rome and back, and a much narrower focus, delving inside the minds of two people - a single mother and her son, Lawrence, who tells the story with the erratic spelling and language of a nine-year-old.

He and his little sister Jemima are whisked off to Italy by their mother, Hannah, because she believes her ex, their father, is stalking them. Lawrence is a precocious young carer - alternately protecting his mother and entertaining the baby, the next minute descending into a childish tantrum.

He unquestioningly absorbs his mother's belief that her ex has followed them to Rome and is watching them from the opposite building. Adult readers begin to doubt this, particularly when the stalker starts putting knives in Lawrence's bed and poisoning the water, turning everyone they know against them.

At first the child narrator seems unbearably cute, inviting unfavourable comparison with another Oxford author, Mark Haddon, who somehow made us believe that The Curious Incident of the Dog in the Nighttime was written by an autistic teenager.

However, the cuteness is offset by Lawrence's obsessional - and completely believable - passion for astronomy and Roman emperors, as pertinent facts about his hobbies illuminate the strangeness of adult behaviour. The final pages left me in tears as Lawrence, after devising a plot to stop the stalking for ever, discovers the full extent of his mother's betrayal of his trust. A moving depiction of mental illness and its impact on a family.