Frances Cairnes begins her search for the person who killed her six-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 coax her way 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 - she's found her weapon. Things heat up for DI Strangeways as he becomes ever more convinced of the possibility of foul play.

Frances looks set to exact her revenge, when an unexpected turn of events threatens to derail her plans. Having uncovered further leads into Frances' unsolved case, DI Strangeways' strategy is blindsided by a surprising discovery.

Frances struggles to deal with the fallout of her attempt to punish the man who killed her son. Strangeways scrambles to find answers before it's too late.