Back in Africa, Thomas had not given up. Left for dead in the desert, he had been found by a group of nomadic Tuaregs. Driven by a guilt that burned hotter than the sun, he sold everything he owned to hire a guide—a man who knew the "Shadow Paths" of the slave trade.

"You," he said in a low, gravelly voice. "The Sheik has been looking for a prize like you. Rare. Educated."

The next morning, the landscape shifted from the green fringes of the south to the harsh, orange expanse of the desert. Their jeep kicked up a trail of sand that could be seen for miles. They were only hours from the border when the sound of an engine—high-pitched and frantic—echoed behind them.