Welcome to Pemfort review – shattering study of living history and the past you can’t shake off

Everyone is trying their best at the Pemfort Castle gift shop, where hundreds of years of history are smoothed down to plastic goblets and dragon slippers. Around designer Alys Whitehead’s carefully curated set of wooden swords and jars of jam, Sarah Power’s shattering new play uses a living history event to grapple with the stories we tell about – and to – ourselves, and question what happens when the past cannot be shaken off.

“Medical leeching demonstration” is pinned optimistically to the ideas board for the sleepy castle’s forthcoming event, which accuracy-oriented Glenn (a serious, wonderfully pernickety Ali Hadji-Heshmati) desperately wants to be a success. He is outraged at the suggestion by scatty Uma (Debra Gillett, oozing warmth) that they lump together the dark stories of the castle’s past, out of time and context, while Ria (a buoyant Lydia Larson) is happy to go along with it, her mind half on the local deer she is in the process of befriending.

Tenderness coats this play like wrapping paper, which Power bides her time to tear away. We are lulled into the idle chatter of her beautiful bunch of oddballs, when the arrival of former offender Kurtis (a tremendous, crumpled Sean Delaney) throws the team into disarray. With an open heart and gentle manner, you can feel him thinking everything through before he says it: wanting to please Glenn, make Uma proud and, above all, make Ria laugh.

Tender … Ali Hadji-Heshmati and Sean Delaney. Photograph: Tristram Kenton/The Guardian

But when Kurtis reveals his violent past, everything shifts. It is as though he is joined on stage by his former self and no one knows which one to address. Power doesn’t give any easy answers about how to feel about Kurtis, nor about what his future looks like, and Delaney gives a haunting performance of a man splintering from shame.

Director Ed Madden lets the script’s silences sit, laying out the revelations and their consequences and waiting as we make up our minds about them. In the meantime, there is a re-enactment to rehearse for, because you only need to wait several hundred years before an act of terrible violence stops being a tragedy and becomes entertainment instead.

• At Soho theatre, London, until 18 April.