From his days spent in trenches during the Great War in France, Ray “Fos” Foster had always been intrigued by light. Upon his return to the United States, Fos sets up a photography studio with his new wife, Opal. When Opal inherits land in rural Tennessee, the two relocate, but are soon forced to pick up again after the land is claimed by the Tennessee Valley Authority in 1942. Fos’ scientific leanings lead him to seek work at the Oak Ridge Laboratory, where the government is secretly pushing full force ahead for the construction of the atom bomb that eventually will be dropped on Hiroshima. But when Opal is struck with radiation poisoning, Fos loses his faith in science and realizes the difference between things of natural radiance and the new world of artificial suns – a realization that will ultimately come to haunt his son.