A peace march in Londonderry erupts in mayhem on Assumption Day, 1970, and the embattled Royal Ulster Constabulary summons Chief Inspector Jack Hamilton.
In the aftermath he sees curls of auburn hair gently waving in the drainage water between riot-damaged cars. He discovers a young lady who arrived to her death fashionably dressed. Her glazed eyes look curiously skyward and her mouth is slightly open, as if she forgot a question.
The victim in this march threatens an unstable truce. Can the inspector find her killer before tensions burst between a Protestant militia and a Catholic rebellion willing to tear Northern Ireland apart?