Mortal Sin - Edinburgh Fringe Festival 2026

​Benjamin Reilly’s Mortal Sin, performed by Reilly as Colm alongside Isolde Fenton as Peggy Kelly, is a heartbreaker of a play. On the surface, it is a funny, tender story about two fifteen-year-old best friends in rural Ireland in 1963 who decide to stage a protest to get a day off school to mark the assassination of JFK. But beneath the warmth, laughter and beautifully realised performances, there is a constant spectre of death, repression and the loss of innocence hanging over everything.
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Set in a fictional Irish town that will feel instantly familiar to anyone who grew up in a small community, Mortal Sin captures a place where gossip travels faster than truth and secrets drift through the streets like a “sea breeze”. This is an Ireland where you were “a Catholic first, Irish second”, and where the Church’s influence extended from the classroom to the confessional and into the home. Being different was not something to celebrate, but something to survive. Colm and Peggy’s decision to “stick it to Sister Assumpta” is therefore more than an excuse to escape school. For Peggy, who longs to live somewhere where something actually happens, the protest becomes a small act of rebellion against a world that feels determined to keep everything exactly as it is.

That rebellion is particularly poignant because death is never far away. JFK’s assassination carries an unusual weight in Ireland. Kennedy was not simply a distant American president. As the first Catholic U.S. president, his Irish heritage and historic visit to Ireland only months before his death had made him a figure of enormous affection and pride. Reilly cleverly allows that public grief to sit alongside the much smaller losses of childhood. Even Elvis the mouse is not spared. These moments are funny, but they accumulate, creating an increasingly powerful sense that the world Colm and Peggy inhabit is one where innocence can disappear with startling speed.

And the institutions surrounding them are not simply background. The Church casts a sinister shadow over the town, but Reilly makes its control painfully personal through Colm’s father, who attempts to scrub the gay out of his son. The play understands that oppression does not always arrive through grand gestures. Sometimes it is found in a look, a confession, a whispered rumour or the expectation that you should know which parts of yourself must remain hidden.

Fenton and Reilly are exceptional in making these two fifteen-year-olds feel completely real. There is never a sense that older performers are simply playing children. They capture the awkwardness, mischief and complete sincerity of adolescence, but also the suppression of feelings that neither character yet has the language to articulate. Their friendship becomes the emotional centre of the play, a space where they can be themselves even when the world around them insists they should be something else.

Mortal Sin ultimately belongs to Colm and Peggy. Their protest may be small, their town may be fictional and their rebellion may seem almost comically insignificant, but that is precisely the point. In a society where so much power is held by institutions that tell you who to be, choosing friendship, curiosity and the freedom to be different can itself become an act of defiance.

The epilogue brings the spectre that has hovered over the play decisively closer, and it is genuinely heartbreaking. What begins as a funny and affectionate story of two friends becomes something much more devastating. You leave Mortal Sin feeling utterly broken, but also incredibly lucky to have witnessed Fenton and Reilly together. Their performances are beautifully judged, their friendship feels completely authentic, and there is a real excitement in knowing that this is hopefully only the beginning of what both can do, together and apart.

Lee Hutchison
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4/5

Runs until August 31st at the Gilded Balloon