David, Rosalind, Petra, and Michael go to the Fringes after they are exposed as deviants.
David’s society is one in which an apocalypse of some kind has left everyone so frightened of offending God that they look for deviancy everywhere. If anyone is the least bit different, the person must go. They do the same thing even with valuable plants and livestock. Babies are left to die, and people who are discovered later to have a Deviance, some kind of unusual feature, are expelled from the community into the Fringes. Women are sterilized and men are outlaws.
David and the others have an unusual deviance. It is not like the one he noticed on his friend Sophie, who had an extra toe. That could be noticed. Their deviance could not be seen. They could read minds.
Such a deviance could go years without being detectable among the community. In fact it did. It wasn’t until they were discovered when they had to fight back. Rosalind even attacked the man who tried to capture her. She killed him. They realized they were found out because Katherine had been caught and tortured for information.
Michael explained why the people were so worried about the telepaths.
But what's got them so agitated about us is that nothing shows. We've been living among them for nearly twenty years and they didn't suspect it. We could pass for normal anywhere. (Ch. 12)
To have a group of telepaths was more worrisome to them, even than the other deviants. Thus the telepaths had to flee to the Fringes where the outlaw society was. There they saw David’s father’s older brother, Gordon, whom he called a “spider-man.” He is in charge. He threatens David until he tells him how many men are coming for the telepaths. Gordon still resents losing his inheritance.