It's 1989, and in a Belfast torn apart by conflict and terrorism, petty criminal Marty McGartland is recruited by the British police to infiltrate the IRA. Guided by Special Forces officer 'Fergus', McGartland gains unparalleled insight into the organisation's dealings, providing his British handler with priceless, life-saving information. Based on a true story.

Violence erupts in north Belfast when the residents of Glenbyrn, a predominantly Protestant suburb, object to schoolgirls walking through their neighbourhood from the Catholic area of Ardoyne to the Holy Cross primary school.