The genocide directed by the Hutu majority government against the Tutsi population in Rwanda lasted just 100 days in 1994, yet up to a million Rwandans are estimated to have been killed. It occurred when, in the west at least, we were basking pacifically under the blue skies of the End of History, with the collapse of the Berlin wall dispelling cold war anxiety, perhaps for good. This act of genocide was a reminder of how easily humanity can recoil into barbarism.

Hugo Blick, previously responsible for the likes of The Shadow Line, set himself the invidious task of converting this subject matter into BBC drama, with all its protocols, demands and constraints. He pulled it off magnificently, by his shrewd approach to storytelling and to the unorthodox styling of the show, and with the excellent assistance of a cast that included Michaela Coel, John Goodman, Harriet Walter and Blick himself, as the brilliant but unpleasant lawyer Blake Gaines.

Black Earth Rising tells the story of Kate Ashby (Coel), adopted daughter of Eve Ashby (Walter), a barrister working in international justice with a particular interest in Rwanda. Kate was rescued during the civil war – she has no idea of her real name but a strong sense of her Tutsi identity. She has experienced mental health issues and is now back working as a legal investigator in the chambers of UK-based American lawyer Michael Ennis (Goodman).

Facebook Twitter Pinterest Intrigue and uncertainty … John Goodman in Black Earth Rising. Photograph: BBC/Forgiving Earth Ltd/Des Willie

Kate’s mother was extremely supportive during her breakdown but nonetheless she feels betrayed to her core when Eve takes on a case to prosecute a Tutsi general for war crimes. Of all the people to go after, she picks on one of the heroes of the Tutsi liberation? Eve never gets to explain herself – shockingly, she is shot dead by an unknown assassin in the Hague.

What follows is a drama of intrigue, uncertainty and confusion for Kate, as she is called on to help defend Alice Munezero, half-sister of the current Rwandan president and another war hero, who has been extradited to France on a charge of killing a priest. The more Kate investigates, the more she learns, and the more we feel that something of great significance is being kept from her: a conspiracy involving Ennis, Munezero and US State Department bigwig Eunice Clayton, as well as her late mother and father. When the truth finally emerges about her true identity, and the reason for her being kept in the dark all her life, it is as big and wrenching a twist as any on TV this year.

Facebook Twitter Pinterest Star turn … Michaela Coel in Black Earth Rising. Photograph: BBC/Forgiving Earth Ltd/Des Willie

Coel is superb as Kate – required to be both tough and fragile. Beneath her determined, sardonic carapace lies a bereaved, lonely and bewildered soul, whose lack of memory of 1994 somehow adds to her pain. Her relationship with Ennis is a complex one; intimate and distant, father and daughter but also, briefly on her part, romantic. And beyond Ashby’s central role is a hinterland of moral and political complexity, of pragmatism and neo-colonialism, and a burning sense of national pride that deeply resents western condescension.

One of Blick’s many masterstrokes is not to address the unimaginable brutality through gory re-creation but through shrewd use of animation – the genocide, like the sun, should not be stared at directly, yet not shied from. “Dark” drama has become wearisome in recent years, often bogus confections involving serial killers adjacent to lakes or far-fetched conspiracies that go right to the top. Fictional as it is, at the dark core of Black Earth Rising is the very real and most brutal event of modern times, one that remains not entirely resolved.