Towards the end of this endearing novel, Jenny the Elephant has joined Cross's Famous Menagery as one of the many exotics who entertain the crowds of 18th-century London for as long as their health permits. (The lions in particular never last long.) Mr Cross devises for each animal a tale to increase its mystique; above Jenny's cage a notice announces that "The Empress" was born "in the court of an Indian prince, whom she often carried on tyger-hunting expeditions, displaying great bravery. She was captured after a long battle and brought to Europe." Tom Page, her loving keeper and the narrator of Christopher Nicholson's second book, objects, but Cross reminds him that "people like stories. So long as the stories are possible, it does not matter whether they are true or false". It's a moment of rueful self-consciousness in a novel that spins a complicated tale from a speck of fact. Although Cross is a mercenary pragmatist who teaches monkeys to smoke, he shares with his author an awareness that what matters is not the literal truth of a story but its spark of possibility.

Jenny's "true history", as (almost entirely) invented by Nicholson, is less exotic than that of her Empress alias, but does indeed contain battles and travel. Captured in the East Indies, in England she endures cruelties from which Tom can only partly shield her. Jenny's constant, saintly fortitude is a problem; even when she finally feels obliged to crush a rapist to death we are cheated of any satisfying sense that she has, for once in her long life, lost her rag. Like that founding fiction of the animal-rights movement Black Beauty, this moral tale depends on the animal being infinitely more humane than the humans.

This lifelong partnership between elephant and obsessively zealous keeper may owe something to a well-documented Victorian story: that of Jumbo and Matthew Scott, who moved together from London Zoo to Barnum's circus. But The Elephant Keeper has other antecedents too: from slave narratives to post-colonial fictions about the knotty relations between oppressor and oppressed. Sometimes it seems less a novel than a rich meditation on the Enlightenment: its rationality and superstition, silly games and serious concerns.

Like the elephant at its centre, Nicholson's book is gentle, profound and sweet-natured. If the first half is rather too discursive - including more measurements of parts of elephants than most readers will care to absorb - then by the second half, we find ourselves fascinated by a marriage like no other.