It’s 1843, and along with hundreds of his fellow ministers, Reverend John Ferguson has broken away from the Church of Scotland to form a new denomination. His zeal is dented only by the worldly question of how he and his wife, Mary, are to survive without his stipend, which is why he agrees to sail to a tiny island halfway to Norway. Dispatched with scanty provisions and a pistol, he must inform its lone inhabitant, a crofter named Ivar, that he’s to be evicted as part of the Highland Clearances.

So begins Carys Davies’s third novel, Clear. But while the story is set in motion by two mighty upheavals in Scottish history, the book’s driving source of fascination – language itself – is revealed only once John reaches the island.

Shortly after arriving, John takes a bad tumble off a high, rocky path. He’s found, barely conscious, by hulking, straw-haired Ivar who, relieved of his long solitariness, chooses not to speculate about this pale stranger’s intentions. They have no common tongue, but slowly, as John recovers, he begins piecing together a glossary of Ivar’s vocabulary.

Davies borrows from Norn, a vanished language once spoken on the islands of Orkney and Shetland, whose specificities it evolved to pin down. There are many words, for instance, to describe stormy seas (gilgal, skreul, pulter, yog) and gradations of grey (emskit, dombet, broget).

Her own language is a marvel of eloquent restraint, as when a ray of sunlight falls in Ivar’s bothy “in a slowly turning, glittering column of chaff and fish scales and wisps of floating wool”. Ivar’s entire hard yet transcendent life is there.

But what of John’s mission? What of his pistol? On occasion, this intimate, lean three-hander seems ready to lurch towards melodrama, but it always pulls back. If there’s a flaw, it lies in the characterisation of Mary, aged 43 and a late bride, but otherwise overly determined by two other snippets of history whose quirkiness swamps any nascent sense of her: the advent of false teeth and the Comrie earthquakes.

And yet it’s Mary, growing anxious on the mainland, whose bold actions will carry Davies’s memorable novel to its unexpected, delicately radical end – an end that conjures new, shared beginnings in which John’s growing list of words becomes “like a prayer, or a gentle weather forecast”.

• Clear by Carys Davies is published by Granta (£12.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply