Flambeau (John Light) is incarcerated under suspicion of murder. When Father Brown (Mark Williams) visits him he denies killing his cohort Flynn (Callum Dixon) and asks the priest to hear his confession if he's convicted. Flynn's wife Peggy (Emma Pallant) later tells Father Brown that she witnessed Flambeau dragging Flynn's body to the river and throwing it in. At the presbytery, Mrs McCarthy (Sorcha Cusack) thinks that Flynn is still alive and has framed Flambeau. Father Brown leaves the surveillance to her and Bunty (Emer Kenny) while he attends Flambeau's pre-trial hearing. He's shocked to hear Flambeau plead guilty then be sentenced to death by hanging. Meanwhile, Bunty and Mrs McCarthy spy Flynn through the window at Peggy's house and manage to escape after they're seen. However Father Brown has realised that Flambeau isn't the victim in all of this, he's the architect. But what if his plan backfires?