Then she stood up and prepared for the next patient.… The rain had stopped an hour before dawn, leaving the camp wrapped in wet heat and the smell of chlorine, mud, diesel fuel, and human waste. From the observation tower near the perimeter fence, the refugee settlement looked almost infinite. Tens of thousands of white tarpaulin shelters spread across the volcanic plain beside the border, stitched together by narrow drainage ditches and corridors of trampled red earth. Aid agencies called it a “transitional humanitarian zone.” The soldiers guarding the access road called it “Sector Nine.” The people living inside it called it nothing at all. Most had stopped naming places after the third displacement. Tess van der Meer adjusted the elastic band of her KN95 mask and pushed aside the flap of the oncology tent. Inside, the heat was worse. The solar batteries had failed again overnight. The oxygen concentrator stood silent besid...