On an icy morning, a mother wakes to find her daughter's blood-soaked body frozen to the road. Who would carry out such a killing on the victim's doorstep? Straight off her last harrowing case, Detective Erika Foster is feeling fragile but determined to lead the investigation. As she sets to work, she finds reports of assaults in the same quiet South London suburb where the woman was killed. One chilling detail links them to the murder victim - they were all attacked by a figure in black wearing a gas mask. Erika is on the hunt for a killer with a terrifying calling card. The case gets more complicated when she uncovers a tangled web of secrets surrounding the death of a beautiful young woman. Yet just as Erika begins to piece the clues together, she is forced to confront painful memories of her past. Erika must dig deep, stay focused, and find the killer. Only this time, one of her own is in terrible danger.