On a starry night in August 2015, Ranim Alsous and her three children set out across one of the deadliest straits of the Aegean Sea. Alongside fifty other refugees of many ethnicities and sects, Sunni and Shia, Arab and Kurdish, they climbed into a small dinghy — really nothing more than an oval of inflatable plastic with a motor attached — near Bodrum, off the southwestern tip of Turkey, and headed for the Greek island of Kos.

The journey started smoothly. Turkish authorities were nowhere to be seen, the waters calm, the air warm. In less than an hour, the family would…