Some 96 km south of Varanasi, the late autumn afternoon sun setting over the low-lying Vindhyas, opulent forests and the winding Son river defining Sonbhadra’s rich tapestry of landscape, nothing warns you about the long night that is Bagesati. Sonbhadra is the second largest district of Uttar Pradesh, a panhandle in its southeast, sharing a border with four other states—Madhya Pra­desh, Jharkhand, Chhattisgarh and Bihar—and Bage­sati is, well, a village on all fours.

Eerie darkness looms overhead, below it’s a scene straight out of Zombieland. People amble by slowly, bent, stumbling, their gazes vacant, overcome intermittently by uncontrollable tre­mbling. Sandhya, 14, is sprawled on the floor of the courtyard outside her tenement, unmoving, lifeless, detached, just staring out with glassy eyes. “The abnormal one,” her parents tell everybody. “She was such a sprightly kid,” says her father Jagjivan. “But for the last six-seven years, she has been complaining of severe joint aches, numbness and...