It is a dark winter’s night in Belgium, a country where the suicide rate has been called “dismally high”. Suicide is an awkward subject, but director Milo Rau is not one to shy away from society’s ugly corners. Mesmerising and alarming, Familie completes a trilogy that began with Five Easy Pieces, in which children told the story of child molester Marc Dutroux, and La Reprise, which reconstructed the murder of Ihsane Jarfi in a random act of homophobic violence.

This play also takes its template from real life. In 2007, the four members of the Demeester family were found hanged in their Calais home. They had a meal ready to eat and left no sign of struggle. The only clue to the joint suicide of this comfortably off family was a terse note: “We messed up. Sorry.”

It’s not much to go on, but Rau turns the enigma into a strength. Working with a mix of professional and amateur actors in accordance with his 10-point Ghent Manifesto, he enlists a real family to imagine the fateful final night. Prominent Belgian actors An Miller and Filip Peeters are joined by their teenage daughters Leonce and Louisa Peeters, plus dogs Billy and Bobby, in an evening not of histrionics and grinding of teeth (for that, Rau would direct you to Romeo and Juliet), but of heartbreaking banality.

Guilelessness … Familie’s real-life family cast. Photograph: Michiel Devijver

The production it most closely resembles is Vanishing Point’s Interiors, a dark domestic comedy performed behind the windows of a single-storey house that turned the audience into unwitting voyeurs. Likewise, Anton Lukas’s realistic set for Familie allows dad to get on with the cooking, mum to call her parents and the kids to do their English homework as if, for the most part, we’re not there. Moritz von Dungern’s deftly integrated live video projections pull us closer to their everyday routines. One section is called “Killing Time”.

By rights, a play shorn of everything we expect of a night out – drama, conflict, debate – should be excruciating, but such is the guilelessness of the four actors, the apparent spontaneity of their stage life and the excruciating tension of knowing their fate, that the mundane becomes riveting. In its opening and closing sequences, the cunningly crafted piece reels off lists of private pleasures: watching movies on a rainy day, doodling during a phone call, reading Harry Potter… On their own, they are whimsical and insignificant, but cumulatively, they are the reason we keep on keeping on, our way of defying existential despair.

We love this family in the way we love the talking heads on Gogglebox, not for their exceptionalism but the very reverse: their ordinariness and lack of pretence. That we are seeing enactments of real family relationships in parallel to the true-life tragic tale adds to our distress.

Everyday banality and no ‘to be or not to be dilemma’ … Milo Rau’s Familie. Photograph: Michiel Devijver

Rau does not concern himself with fathoming a meaning behind the suicides; there is no “to be or not to be” dilemma. He accepts the Demeesters’ actions are unknowable. Even with more information, we would still find their deaths inexplicable. Where would guessing get us?

Instead, he offers us a kind of dark, secular mass, at once a celebration of all life has to offer in its smallest, most trivial moments, and a painful recognition that sometimes it can be too much. Performed at the stately pace of a slow piece of Bach, Familie is assured, soulful and unnerving.

• At NTGent, Ghent, Belgium, until 22 May.

• In the UK, Samaritans can be contacted on 116 123 and the domestic violence helpline is 0808 2000 247. In Australia, the crisis support service Lifeline is on 13 11 14 and the national family violence counselling service is on 1800 737 732. In the US, the suicide prevention lifeline is 1-800-273-8255 and the domestic violence hotline is 1-800-799-SAFE (7233). Other international helplines can be found at www.befrienders.org

