Mother's story makes waves at Southbank's Women of the World festival

We took the last bus, the last bus of the evening, so no-one would see us." So begins Beside the Sea, an extraordinary, intense novella by the French playwright Véronique Olmi that the young Irish actress Lisa Dwan is translating to the stage in a solo performance as part of the Southbank's Women of the World festival.

Dwan scored a hit at the same event last year with her sensational performance of Beckett's Not I, a floating mouth monologue she describes as "falling backwards into hell, emitting cries".

That torrential piece was discharged in just nine minutes and 50 seconds the night I saw it. Beside the Sea, which is directed by Irina Brown, stretches to almost an hour, which should be time enough: this is a tale of a modern Medea who takes her two small boys on an outing to a dismal small town resort with no intention of bringing them home.

It seems we read about infanticide every day in the newspapers. Sixty per cent of the perpetrators are men, the crime mostly relating to child abuse and violence. The women are mostly mentally disturbed and feel, as does Olmi's nameless protagonist, that they are committing an act of altruism in saving their children from the wicked world.

"This is a woman," says Dwan – who hails Athlone, County Meath – "who takes the act of love to the final conclusion. There's no 'reveal' as an actor – we know what will happen – so the challenge is to keep the layers interesting."

Beckett never felt that his woman in Not I was unusual. She existed on every road in Ireland. Dwan feels the same about Olmi's character: "People fall through the social cracks before they know it. None of us can afford to be too haughty. The voice in Not I wasn't a mad woman to me. She felt like a photo of my insides."

'Beside the Sea', Purcell Room, Southbank Centre, London SE1 (www.southbankcentre.co.uk), 7 & 8 March