The American government was faced with an unprecedented challenge: where to house the nearly 400,000 German prisoners of war plucked from the battlefield and shipped across the Atlantic. On orders from President Franklin D. Roosevelt, the Department of War hastily built hundreds of POW camps in the United States. Today, traces of those camps—which once dotted the landscape from Maine to California—have all but vanished. Forgotten, too, is the grisly series of killings that took place within them: Nazi power games playing out in the heart of the United States.

Protected by the Geneva Convention, German POWs were well-fed and housed. Many worked on American farms, and a few would even go on to marry farmers’ daughters. Ardent Nazis in the camps, however, took a dim view of fellow Germans who befriended their captors.

Soon, the killings began. In camp after camp, Nazis attacked fellow Germans they deemed disloyal. Fifteen were sentenced to death by secret U.S. military tribunals for acts of murder. In response, German authorities condemned fifteen American POWs to the same fate, and, in the waning days of the war, Germany proposed an audacious trade: fifteen German lives for fifteen American lives.

Drawing on extensive research, journalist and author William Geroux shines a spotlight on this story of murder and high-stakes diplomacy, and on the fifteen American lives that hung in the balance—from a fearless P-51 Mustang fighter pilot to a hot-tempered lieutenant colonel nicknamed “King Kong.”

Propulsive and vividly rendered, The Fifteen reminds us that what happens to soldiers after they exit the battlefield can be just as harrowing as what they experience on it.