Two Irish men sit on opposite sides of a prison wall in Dublin. Inside the cell is Frank, a republican pacifist who refuses to join the Easter Rising. Outside stands Anglo-Irish teenager William, a new recruit to the British army. The two cannot see each other but they listen to, laugh with and console each other. By the end of Lizzie Nunnery’s fine new play, Frank will have died on William’s watch. It is just one of countless stirring scenes in a song-led show that boils over with the chaos of war.

Nunnery has a strong track record of working with historical material and creating something that feels fresh and dynamic on stage. To Have to Shoot Irishmen is based on the real-life murder of Irish pacifist and Manchester Guardian journalist Francis Sheehy-Skeffington. Nunnery wears her research lightly and expresses her ideas in tumbling poetry, lively dialogue and haunting song. Not a syllable or beat is wasted. Director Gemma Kerr’s production never feels overstuffed and there is an easy rhythm to almost every scene.

Robbie O’Neill, Gerard Kearns, Elinor Lawless and Russell Richardson in To Have to Shoot Irishmen. Photograph: Tristram Kenton/The Guardian

The songs have been co-written with Vidar Norheim and tingle with the hope and desolation characteristic of Irish folk music. The excellent four-strong cast sing in fragile unison. Frank (Gerard Kearns) sits at the piano, which stands above a barricade of rubble in Rachael Rooney’s elegantly shattered set. Frank’s wife, Hanna, played by a steely Elinor Lawless, sings in the shadows while Russell Richardson’s stiff British army general taps out disjointed rhythms among the rocks. The harmonies tease us; they promise a warm resolution that will never be found.

And then there are the images, vibrant and shocking. Frank describes a boy who is shot while happily waving the Irish flag: “As he turned from gleaming show to flesh – to parting flesh.” He recalls his young son pretending to play chess, mechanically repeating the moves of his father: “He hadn’t a clue how to play the game but he knew for certain he had to frown while he did it.” Just like that, the hereditary nature of war is revealed.