Silver, By Andrew Motion

The best books are written with an ear to somebody. Treasure Island was written in 1883 for Robert Louis Stevenson's 15-year-old stepson, Lloyd Osbourne. It was intended to be a boy's book in the mould of RM Ballantyne's Coral Island, Captain Marryat's Masterman Ready, and Fennimore Cooper's The Last of the Mohicans, ripping yarns all. It succeeded beyond Stevenson's wildest dreams, becoming a cornerstone of childhood literary memory, indirectly inspiring masterpieces as different as Peter Pan, Swallows and Amazons and High Wind in Jamaica, and directly spawning a dozen forgotten prequels and sequels.

Now Andrew Motion enters the lists with a high reputation and a solid following behind him. Does Silver: Return to Treasure Island work? Yes and no, has to be the answer. The former Poet Laureate acquits himself flawlessly for the first 50 pages, and offers much splendid invention throughout. The tale opens in the Hispaniola, not the ship in which Jim Hawkins sailed in search of Captain Flint's treasure, but the tavern on the north bank of the Thames near Greenwich which Motion's Hawkins bought in the 1780s with the last of his Caribbean spoils.

Thirty years on, our hero is his son, also Jim, who, because of the death at his birth of his mother, "grew up in an atmosphere stained by melancholy". Jaded by the tedium of his work in the inn and at the eternal repetition of the legends of Treasure Island, he takes most pleasure meandering in the river's marshy edgelands. Then the entrancingly beautiful and competent Natalie rows out of the mist, tells him that she is the daughter of Long John Silver and his "woman of colour", and asks Jim to steal the map so that he and she can sail to win the "bar silver" that Stevenson, perhaps with half an eye to a sequel of his own, told his readers was left on the island.

So far, so very good. Motion adopts pitch-perfect Stevensonian prose, and excels in grippingly detailed description, as when Jim destroys a wasp's nest or raids Billy Bones's battered sea-chest for Flint's map of the island. He rivals Conrad in symbolically freighted descriptions of the estuarial Thames. The scene in which Natty takes him to the Spyglass, her own family's rickety, ship-like Wapping tavern, to visit the emaciated ruin of Long John Silver, now blind as Pew, is superb. Strains of gospel song come from her mother downstairs, Silver runs his clawlike fingers over Jim's face, his voice is "a hiss of steel, like a sword being pulled from its sheath".

But Long John is left behind, we find Motion's new villains less satisfying than Stevenson's, and disbelief only precariously suspended. Would Jim, should Jim, steal the map from his father and without a word of goodbye set sail with Natty, now disguised as a boy, in a ship crewed by Silver's hirelings? When the treasure-seekers discover Stevenson's maroons living in unspeakable depravity, would Natty disappear into the island with the mysterious Scotland, muttering that he and she are of a kind?

Things work, just, in the end. The storm on the island and the hurricane that assails the loaded treasure-ship make nail-biting reading. But who, one has to ask, is the book for? Not children, I think. Silver is not the kind of modern boy's book that Anthony Horowitz and Philip Reeves dash off with unerring panache. But nostalgic lovers of Treasure Island, who are after all legion, will devour it eagerly, enjoying the range both of faithful reference and jokey nudges, most egregiously a seaman "by the name of Mr Stevenson – a Scotsman and a wisp of a fellow, whose place was generally in the crow's nest".

Christina Hardyment's 'Malory' is published by HarperCollins