The Book of Lights is divided into three sections. The first details the seminary days of Gershon Loran and Arthur Leiden at Riverside Hebrew Institute in Manhattan. The second section follows Gershon in his year of chaplaincy duty in Korea right after the war. The third is a moving account of the visit to Kyoto and Hiroshima by Gershon and Arthur who are now reunited.

After his parents were killed in terrorist cross fire in Palestine in 1937, Gershon was taken in by his aunt and uncle. His aging uncle, afflicted with emphysema, attempts to run the decaying apartment house in which they live. The surrounding Brooklyn neighborhood is itself decaying, and there are frequent fires. Gershon is reared in pious Judaism but chooses to attend the nonorthodox Riverside Hebrew Institute. There he is introduced to the academic study of Jewish mysticism by one of his professors, Jacob Keter. Gershon’s plodding, unorganized ways as a student give way to a fervency in his exploration of what Keter called the feeling side of Judaism.

Arthur Leiden becomes Gershon’s roommate at the institute. Arthur, a Harvard graduate, had fled his studies in physics for the rabbinate. He is disorganized, taciturn, with something strange inside waiting to explode. Arthur comes to depend on “dear Gershon” for help in his studies.

Gershon comes to the institute at the outbreak of the Korean war; even after the war has ended, there remains a great need for chaplains for American military personnel stationed in Korea and elsewhere. Indeed, as a condition of graduation, those in the institute are required to make themselves available to the chaplaincy corps. Gershon, without understanding why, volunteers to serve in the army. Nevertheless, his entrance into the service is delayed a year because the institute awards him the first Leiden prize.

The award is named after Arthur’s brother, who was killed during World War II. Gershon learns that Arthur’s father, Charles Leiden, had worked closely with Albert Einstein and other scientists in the development and testing of the first atomic bomb. In retrospect, Gershon realizes that during their seminary days together, Arthur had been haunted by the destructive death light which his father had helped unleash. Arthur had recommended to his parents that Gershon be the first recipient of the Leiden prize.

The award provides a year’s deferment from the service, and Gershon spends the time in study of the Jewish cabala with Jacob Keter. Central to that collection of mystical writings is the Zohar, a series of books describing God and his creation in terms of emanations, the pure radiance of God.

Gershon, after his year of study with Keter, becomes the only Jewish chaplain in Korea, for a time assigned to a medical unit north of Seoul. The debilitating snow and intense heat of Korea provide stark contrast to the sheltered environment of the institute, but for Gershon the experience is a transforming one. Though he continues to study cabala and frequently visits with Keter in visions, his chaplaincy is an active one. He becomes sensitive to his men and is well liked. His management skills and frequent trips to serve other units result in front page write-ups in Stars and Stripes, a boost in the morale of the medical unit, and Gershon’s eventual transfer to division headquarters. There, he learns that chaplain Arthur Leiden has arrived in Korea.

Arthur is desperate to get to Japan, to visit Kyoto and Hiroshima. When the navy refused to provide Arthur with a security clearance (he had signed some left-wing petitions in college), he managed to get accepted by the army. Arthur prevails upon Gershon, and early in 1957 they travel together to Hong Kong and Japan. Arthur is struck by the beauty of Kyoto, its temples and gardens, yet he is filled with darkness when the two enter Hiroshima and stand before the saddle-like monument to those killed in the blast. Arthur searches for words, something to say to atone for the destruction which his father’s work helped bring about. One morning, Arthur stands before the monument and reads from the Psalms, reading of forsakenness and pleading for God’s restoration.

Events move rapidly. Both men return to Korea, but soon Arthur is on board another plane bound for Japan. The plane crashes on takeoff, and Arthur is killed. Later, as Gershon ends his tour of duty in Korea, he visits Arthur’s parents in Boston. They are thankful for Gershon’s friendship with Arthur, and seem themselves to be haunted by the death light. It is here that Gershon learns the secret of Arthur’s love of Kyoto: His mother, an art historian, had indirectly persuaded the government to spare Kyoto, the first intended target of the atomic bomb.

Soon Gershon finds himself in another garden, this time in Jerusalem. He has flown to the home of Jacob Keter, there to study with one of the giants, there to encounter the God of lights.