Wartime Edinburgh: blackout curtains, ration books and Anderson shelters in the gardens of Morningside tenements. But you can travel the city by tram, and on Blackford Hill a farmer's daughter sets snares for rabbits. Agnes Thorne, aged 17, who looks "a bit like Rita Hayworth" and whose mother has a sharp tongue, has been uprooted from rural Ayrshire to become the trophy wife of a handsome if preoccupied academic.

"Once I was a fine Edinburgh lady I wouldn't need to think about the things Mother said, or chickens and sheep and muck." An early warning that this is a capital union doomed to failure.

Victoria Hendry's impressive debut novel wastes no words. The voice of her young narrator is brisk and assured, like youth itself, and the book's title is a neat signal that there's more to Agnes's story than affairs of the heart. Her new husband's attention is divided between his researches into the Scots language and his active support for Home Rule.

These are risky times, internally and externally, for Scottish nationalists; the independence movement is split between pacifists who claim conscientious objection to the war - Westminster's war - with Hitler, and patriots who believe they should fight fascism with the rest of the UK.

Agnes's husband Jeff is on the road to martyrdom and a jail cell, while she is under siege from Morningside locals who want to know why he's not in uniform. This becomes the least of her worries when, troubled by her confused understanding of the principles at stake, she pins her colours to the plight of the stranger in the upstairs flat.

Pity overwhelms politics and the teenage wife, not without ­misgivings, makes a decision which not only affects the rest of her life but her relationship with Scotland. As events move Agnes on from her waspish, forlorn and funny accounts of her attempts to engage with Jeff's academic and political colleagues, the book moves into its most powerful passages.

Hendry demonstrates early skill with language, sketching 1940s Edinburgh with economy. She has a natural feeling for our Scots words - "dreich", "maukit", "keek", "fankle" - and drops them tellingly but sparingly into her narrative, where they break the smooth surface of the English language like flinty pebbles. (Agnes was wooed by Jeff while he was in Ayrshire recording dialect for a Scots dictionary.) But as the story gathers momentum so does Hendry's prose, raising itself to poetry as her heroine confronts that famous tension within Scots and Scotland which many of us recognise:

"As I sat there I hated Scotland …She seemed less like a great beauty, silver rivers of hair trailing over her misty gown, and more like a hag of petrified rock … Scotland ate her own children on winter nights as they dreamed, but each new generation still loved her. She was an unkind parent, a deceiver, a monster; she was a lover, an enchantress, a dream."

A topical novel, then, as we grapple with the multiform identities of Scotland in the approach to 2014, but one in which the political is very much the personal: the coming of age of a young woman whose sometimes acute, sometimes naïve perception of world forces and local conflicts steering her life reaches a cautiously hopeful conclusion, tempered as it is with foreboding for the intractable nature of men and martyrs. A Capital Union is not without flaws, including one or two narrative devices which over-reach themselves, but for a new writer of fiction it is startlingly accomplished.