On the day Karen Sharpe is promoted to Detective Sergeant she loses control and attacks a prisoner she is interrogating. Duly suspended, Karen is investigated and seemingly cleared, but more than a year later the incident still casts a long shadow. When the battered body of a young girl is discovered, it kicks off an inquiry which pushes Karen and a trainee DC, Marcus Roth, too close for comfort, both on and off-duty. The investigation leads to Mary Bradley, currently the carer for a helpless six-year-old boy, Andrew Farrar. As the truth of Mary Bradley's violent past emerges, the inquiry becomes a race against time before Andrew becomes just another one of her child victims. Meanwhile, with the case holding more and more personal resonance for Karen, Marcus discovers that when threatened she has a tendency to ignore the rule book and act on instinct. Before the scores are finally settled Marcus will be wondering whether Karen's legitimate world and Mary Bradley's illegitimate one are really any different.