The Last Sin Eater[1] revolves around Cadi Forbes, ten-year-old girl who lives in a settlement community of Welsh Americans in the mid-1850s.

Cadi is the only one who can see or hear Lilybet, and her parents and others begin to believe that she is "keeping company with taints" and that the girl is a demon.

Despite the danger of being caught, Cadi goes back to talk to the man of God because of her promise to the Sin Eater.

Tragedy strikes in the form of Brogan Kai, who kills the man of God, then turns his fury onto his son, Fagan, seriously injuring him.

Cadi and Fagan escape, eventually, to Dead Man's Mountain, where the Sin Eater Lives.

In the end, Brogan, Fagan, and the Sin Eater have a showdown in front of the entire village at Elda Kendric's house.

Cadi and Fagan, with help from Miz Elda and Iona Kai, reveal the truth to the villagers, and the Sin Eater, named Sim, is free to live as a normal man.