Turley Vail has succeeded in forming an alliance of the northern Circle Villages of Imram. As the new Center, he has renounced the temptations of the Blessing Papers. But the triumph rings hollow as first his lovely wife Jeneen dies, and then his son Thomas grows distant. But when trouble threatens the Circle people, father and son take off together to the south to root out the cause. Through arid valleys and the forbidding Lower Mountains, their journey becomes a battle for the entire human race, and one man's courage becomes the final test for the future of all things in the rise and fall of the Sigma Curve.