It’s around 2pm and Pádraic (Colin Farrell) is doing what he always does, which is to knock on the door of his best mate, Colm (Brendan Gleeson), so they can head off to the pub for a pint of stout. Only Colm won’t answer this time.

He was just sitting there smoking, a bewildered Pádraic tells the barman.

Put simply, Colm no longer wants to be Pádraic’s friend. There has been no falling out, no feuding over trifles. “Well, you didn’t do anything to me. I just don’t like you no more,” Colm tells Pádraic, who keeps wanting to apologise and fix things.

Martin McDonagh, the Irish writer and playwright behind gems like In Bruges (2008), again with Farrell and Gleeson, and Three Billboards Outside Ebbing, Missouri (2017), uses landscape to colour and shape the often-unhinged relationships within his stories. Here, the two men are stuck together on the small island of Inisherin, off Ireland’s west coast.

The island isn’t real but it might as well be. The setting is 1923, and gunfire and explosions over the sea show the Irish Civil War getting underway.

This is an unusual film made powerful by the strength of its cast, built around the towering Gleeson, who has never been better, with Farrell in a more hapless role than we usually see him playing, and Kerry Condon as Pádraic’s sister Siobhán, who wants to take a job in a library on the mainland but dreads leaving her dependent brother behind.

What do you do on an island where you live in each other pockets but are no longer friends?

Colm’s reason for fracturing the friendship is no small thing. He is in crisis over not wanting to live out his days distracted by grinding routine, waiting for the end and never achieving much. He plays the fiddle and is writing a song, “The Banshees of Inisherin”, even though the island doesn’t have banshees, or so he says.

Poor Pádraic can’t understand what he’s done wrong. He thinks of himself as a happy lad, ordinary but nice. He also sleeps chastely in the same room as his sister, loves his pet donkey and has no ambition to speak of.

The plot darkens and McDonagh’s gift for the absurd gets full rein, even as dreadful events unfold. It is a tale of madness, of brotherhood and companionship turned to hate and violence, although not in the way you might expect. As the Irish Civil War rages, the sadness and damage unleashed on Inisherin raises the question whether Colm’s higher ambitions were worth the price of broken peace.

Most of all, it is an acting tour de force from Gleeson as Colm, gripped by despair and the burning wish to wring more out of life, and Farrell’s Pádraic, abandoned and bereft when he asked for so little.

The Banshees of Inisherin opens in cinemas on Christmas Day.