In a Welsh community that has been left behind, a large construction project offers hope for a better future. But an explosion, followed by a catastrophic collapse, leaves many dead, children included, and the community devastated. Polly (Sarah Lancashire) is the wife of the local politician (Mark Lewis Jones) who championed the project. Their rebellious daughter, Leona (Jade Croot) broke onto the site on the day of the explosion, but now is left with a lifelong disability after the disaster. As grief gives way to a torrent of anger and blame, the community finds itself torn apart. It falls to Polly to hold the town together and face the challenging truths that emerge.