After learning the police investigation into the fatal hit and run of her young son, Martie, has been dropped, Frances Cairns takes matters into her own hands. Posing as a novelist researching a murder mystery, Frances ingratiates herself with the family of George Rattery, the cruel and pompous man she suspects is responsible for the death of her son and sets in motion a plan to kill him. She's tracked by detective Nigel Strangeways, who has reason to believe his department covered up George's involvement in the incident. Suffering from PTSD following the recent death of his partner, Strangeways throws himself into pursuing justice for Martie. However, when he discovers Frances living with George and his family, Strangeways finds himself working to both prove George's guilt and head off Frances' plans for revenge before anyone else dies.