A retired teacher is found dead in her Somerset home on a cold January night. At first glance, it is a routine unexplained death and a simple referral to the coroner, until a neighbour reports an unscheduled visit from an occupational therapist an hour before the body was discovered.

Detective Chief Inspector Nick Dixon is convinced the elderly woman has been strangled—a cause of death confirmed by the pathologist—and a murder investigation is launched.

More victims are soon found—a second retired teacher who died in eerily similar circumstances in Devon. Then a possible third victim is exhumed in Dorset.

Leading a regional task force, Dixon must find the connection between the victims. As the coincidences mount, he begins to fear he has stumbled on something premeditated and deeply sinister—a serial killer targeting the elderly in their own homes.