Sister Agnes is about to take her final vows, but is worried about giving up all her earthly possessions. If she ever leaves the convent, how would she survive with no home and no finances? However, Agnes's concerns are put into perspective when Walker McFadden, a lodger at the hostel for addicts in London where she works, is found dead. His brother Alasdair believes the death was no accident and enlists Agnes's help in finding the killer. When she stumbles on Walker's writings of horror and revenge, Agnes feels she is beginning to pick up the trail of truth.