The Little Gentleman

by Philippa Pearce, illustrated by Patrick Benson

160pp, Puffin, £9.99

The last mole who spoke to humans was the cantankerous Mouldiwarp in E Nesbit's The House of Arden, avatar of the Arden family's heraldic badge. Philippa Pearce's little gentleman is wholly mole, or would be if he could.

Mr Franklin, a former schoolmaster enjoying bookish retirement, has a nasty accident with a stepladder and finds himself in plaster. Unable to keep a pressing appointment he enlists Bet, his housekeeper's grand-daughter, to deputise for him. Sent out into the meadow with Charles Darwin's treatise on the earthworm and instructions to read it aloud to no apparent audience, Bet obeys without much question. When it turns out that she is reading to a mole, she is merely bemused. After it emerges from its tunnel "as someone might lean from an open window, settling down on the sill for a gossip with a neighbour" and addresses her, she is as much impressed by the breadth of its vocabulary as by the fact that it is talking. It wants no more visits from Mr Franklin ("vicious and ignoble"), who proposes to keep it in a vivarium - in its own best interests, naturally. Henceforth it will come out only for Bet, and it would like to hear the poems of Alfred, Lord Tennyson.

Mr Franklin, now dependent upon his go-between for news of the phenomenon, begins to realise how little he knew of his mole. Bet, being a child, is conditioned to learn. This is the very mole who raised the hillock over which the horse of King William III stumbled, causing its rider's death and giving rise to the secret Jacobite toast, "To the little gentleman in black velvet". Unearthed, literally, by a Stuart sympathiser at court, he was taken to Scotland as a living talisman to rally supporters to the Cause, and kept alive by means of witchcraft of the Macbeth variety, which also, unintentionally, endowed him with the power of speech. After the rout and massacre of Culloden, the Cause collapsed and the mole, now surplus to requirements, escaped and commenced the only journey in the world that he knew how to make - the way home.

Cursed with immortality, he burrows on and 250 years later has reached Cambridgeshire and Mr Franklin's meadow, having lingered only twice on his way south to enjoy first the company of one Miss X, who introduced him to the works of Tennyson and Darwin, and then that of Master Y, who read to him from the Just William books before growing up and going off to war, never to return.

Bet, too, will grow up and die. ("They all do," the mole says, dismissively; all but the mole.) Her mother has reappeared and claimed her, she has made new friends, looks forward to a new school. The last thing Bet can do for her friend is to help him release himself from the witchcraft to become "wholly mole", even while they both know that this must be the end of the friendship. A natural mole will hate and fear the human. Its loss of speech will be the loss of memory. They must make the sacrifice together.

Although thoughtful editing would have amended a few disconcerting elisions, this is a deeply moving meditation on the transience and mutability of childhood, the necessity - indeed, the desirability - of death at the end of a natural span, and on the painful truth that the highest expression of love is not to possess but to relinquish.

· Jan Mark's books include Useful Idiots (David Fickling Books).