Frances Cairnes begins her search for the person who killed her 6-year-old son in a hit and run; DI Strangeways arrives on the Isle of Wight, hoping for a fresh start after the death of his colleague.

Tracking down the man that she believes is responsible for the death of her son, Frances sets out to insinuate herself into his home as she plots her revenge; struggling to deal with his PTSD, DI Strangeways takes a closer look at the investigation.

Staying on as a house guest, Frances must now work out how she is going to see through her murderous plan; Strangeways' suspicions over his predecessor's handling of Frances' case begin to grow.

As Frances becomes more embedded in the home, she makes progress with her plan and finds her weapon; things heat up for DI Strangeways as he becomes ever more convinced of the possibility of foul play.

Frances is set to exact her revenge, then an unexpected turn of events threatens to derail her plans; having uncovered further leads into Frances' unsolved case, DI Strangeways is blind-sided by a surprising discovery.