Like all good thrillers, the opening of Michela Wrong’s Borderlines reads like a climax. The bad deed has already been done, but the scene’s unexpected pleasure – and that of Borderlines in general – is that when trouble comes it does so with a damp whiff of realism, rather than the pyrotechnics of melodrama one might expect from a novel of political intrigue.

Paula Shackleton, the narrator, is being detained in the airport of an unnamed, troubled African country; she is already contemplating life in a local prison, her mind summoning up disturbing visions of future abuse. Blessedly, as she is a white, British lawyer, she is instead released and sent unceremoniously home to her expat villa in the fictional city of Lira. There, she begins to tell her story.

What follows is an ambitious, multi-layered mystery centered around a legal case: a border dispute between Darrar and North Darrar, the latter a typical fledgling African nation state still reeling from the trauma of colonialism and violence. Paula has been hired by Winston Peabody, a charismatic American lawyer, to work for the government of North Darrar. Sensing that something has gone terribly wrong in Paula’s life, Peabody convinces her that by becoming his assistant, she might do a great service to humanity. Soon the case, played out in an unassuming meeting room in The Hague, escalates with the drama of the best fictional trials: game-changing cross examinations, unpredictable witnesses, the delicate and deadly courtroom warring between two sides.

The novel’s mysteries, however, go beyond mere legal drama. There are historical secrets in North Darrar for Paula to uncover, as she (in particularly delicious moments of revelation) deciphers documents and maps from its history. There are secrets outside the courtroom, too, in clandestine meetings involving the representatives of western governments who, deftly portrayed by Wrong, exude trademark condescenscion and manipulative concern. And then there are the mysteries of Paula’s own past.

Wrong’s greatest achievement is Paula herself. Her voice crackles across the page, compelling and persuasive, witty and charming, sometimes acerbic. She exhibits painful self-awareness, particularly of her presence as a white woman in Africa, yet she is simultaneously naïve, blind to what is really going on around her. If the novel’s bit players sometimes seem to fit into too easily determined roles – the wise African driver who gives just the right advice, the boorish boyfriend of a resentful roommate – they are more than balanced by the complexity with which Wrong imbues Paula and Peabody. Both are intriguingly flawed and deeply broken. Peabody is so compellingly drawn that, via Paula, the reader is star-struck. When certain truths about him are revealed, we feel the sting of disenchantment.

Wrong has an accomplished history of writing non-fiction about African politics. Her debut novel has much to say about Africa in the still unsettled aftermath of colonialism, and even more to say about the western powers who scrambled to divide up the continent and who now seek to influence it for their own purposes. Yet the novel largely avoids the ponderous or polemical (there are just a few moments in which an African character turns up to deliver a timely statement on the west), managing to draw the personal and political themes into a convincing whole. If, at times, it feels like an education, it is one that Wrong makes interesting and urgent.

It is a delight, too, to discover in Borderlines Wrong’s particular gifts as a novelist. Paula’s tightly controlled voice gives way, at carefully chosen moments, to loveliness, as in one memorable scene where she compares the bleakness of North Darrar with the “green promise of glades” and “soft humidity of midge-filled evenings” of her Kent childhood. Sensory details are conveyed elegantly and briskly, and the prose is rich in physicality. In Wrong’s expert hands, the worlds that the novel travels through – government backrooms, refugee camps, the privileged world of expats in “hardship postings” – are sketched with a natural, attractive intimacy.

Borderlines is a novel about relationships, the mysteries they contain, and the ways in which – when they go wrong and leave scars borne across generations – it is often for the most prosaic, petty reasons. This is as true of the relationships between people in the novel as it is for those between governments and their citizens, between nations.

With the pleasure of a good, old-fashioned legal thriller, Wrong illustrates how something as abstract as lines drawn on a map can have human consequences, grand as the horrors of war and oppression, familiar as a broken heart.

FT Kola’s “A Party for the Colonel” was shortlisted for the Caine prize.

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• This article was amended on 25 August 2015 to correct the spelling of Michela Wrong’s name in the headline.

