Charlie Harrison, a former hobo, in his late fifties is settling down to work as a janitor at Idaho State College in Pocatello, Idaho. He has built a cabin on an acreage near the top of Scout Mountain, ten miles south of town, and lives there with his dog Colby. His nephew, Jim Harrison, is intrigued by the Idaho Stories of his Uncle, and upon obtaining his Ph. D. takes his first job as a physics professor at Idaho State.
At first to earn needed money, Charlie also has a weekend job on a potato field. Jim discovers that the soil that his uncle tracks in from the field is radioactive and that starts Jim wondering about the possibility of the nearby National Reactor Testing Station (the "Site") polluting the neighboring country side with stray radioactive waste. Jim becomes even more interested when his Uncle takes a job a the Site because it pays more than the two jobs he had.
Pressures to develop research lead Jim to visit scientists at the Site, where Jim becomes convinced that an employee there has been intentionally following him. Investigating this, leads Jim to have adventures that become increasingly complex and involve the CIA.
One evening while visiting his uncle on Scout Mountain, Jim and Charlie are shot at by an unknown person. However they both suspect that the person driving the car that has followed Jim on several occasions is the shooter.
It slowly becomes evident that the shooter is possibly a Soviet spy who Uncle Charlie had briefly encountered in his wandering past. It seems possible this spy is engaged in trying to sabotage the US nuclear effort during this time of the cold war.
A CIA operative advises Jim as to the dangers of his inadvertent involvement, and the story reaches a crescendo when the spy again tries to shoot Uncle Charlie on Scout Mountain. Colby takes the spy down.
These events lead Uncle Charlie to become disgusted with his settled life and he goes back on the road, leaving Colby with Jim.
