Only the Light Moves tells the story of a twenty-four-year-old US Army pilot who volunteered to fly covert S.O.G., or Studies and Observations Group, reconnaissance missions over the Ho Chi Minh Trail, a region that came to represent not only the United States' war with Vietnam, but also the "secret war" with Laos and Cambodia.

But this is not simply a war story; it is a love story about flying. Captain Francis A. Doherty spent every day for ten months above the jungle battlefield in a Cessna O-1 Bird Dog. The first all-metal fixed-wing aircraft ordered for and by the United States Army following the Army Air Forces' separation from it in 1947, the single-engine Bird Dog was a liaison and observation aircraft. And for this role, it was completely unarmed.

It was from the cockpit of a Bird Dog that Captain Doherty observed this illusive war, perhaps searching out enemy troop movements or calling down waiting F-4 Phantoms to strike a new target. It was a war in which he followed his father's footsteps in his dream to become a pilot, and where he learned a compassion that extended both to his comrades and the civilians caught in the middle of that terrible war.

In Only the Light Moves Captain Doherty only reveals the highs and lows of his year at war in Vietnam but expands beyond his time in the conflict. He explores the emotional struggle he and his comrades faced after they returned home, reconciliations with lost faith, and the incredible impact of war on families.

We are also given an insight into Francis' subsequent journey to becoming a commercial airline pilot. His story makes no effort to glorify the violence that took the lives of so many. There are no broad stroke proclamations about the war, only a very personal, sensitive account of a terrible conflict seen through the eyes of a then young pilot in the air, illuminating the reality and the cost of when one's country decides to go to war.