When Andrew Motion finished Silver, his sequel to Robert Louis Stevenson’s Treasure Island, he promised that it was the first in a trilogy. The next, he said, would be “sort of a western” and as Jim, son of Jim Hawkins, and Natty, daughter of Long John Silver, harness their ponies and stagger into a dusty Texan hotel, one does half expect the crack of a lasso and a bar-room brawl. 

Instead, Jim falls into the first proper bed he’s seen for years. It’s been quite a journey, beginning when the duo crawl on to the coast of “Spanish America” from the wreck of the treasure-laden Nightingale like a 19th century Prospero and Miranda. “Red Indians” have taken them prisoner, scalped the remains of Bo’sun Kirkby and murdered watchman Mr Stevenson. It’s a telling moment: this is no longer a rip-roaring tale of buccaneers and gold. It’s a new world. And everyone is complicit in its moral decline. 

What follows is a road trip of sorts: Natty and Jim escape their captors – but not before being sidetracked by one last greedy grab at treasure – and set out to find the Mississippi, the gateway to a passage home. On the way they meet a group of Native Americans less hellbent on their destruction and Jim has a moment of clarity. “What sort of wrong turn had mankind taken, when it abandoned the life of simple things and open air?” he asks. 

It’s a question Motion repeatedly returns to, perhaps at the expense of a truly adventurous plot. Certainly there is intrigue in Jim and Natty’s pursual across America by the wronged chieftain Black Cloud, but it begins to take on the feel of a videogame. Obstacles – natural, animal and human – are overcome in the knowledge that there will, in the end, have to be a confrontation with the end-of-level baddie. 

Still, that setpiece with Black Cloud is masterfully drawn, capturing Motion’s point that westerns don’t have heroes but single-minded people twisted by their innate selfishness.

The New World is published by Jonathan Cape (£12.99). Click here to buy it for £8.99