Burned by her own government in a trumped-up scandal, brilliant microbiologist Hallie Leland swore she’d never return to the world of cutting-edge science and dangerous secrets. But a shocking summons from the White House changes all that. A mysterious epidemic is killing American soldiers in Afghanistan—and poised for outbreak in the United States and beyond. Without the ultrarare organism needed to create an antidote, millions will die. Hallie knows more about “Moonmilk” than anyone—but it can be found only at the bottom of the deepest cave on Earth. To get there, she and her team of experts must brave a forbidding Mexican jungle crawling with drug cartels, federales, and murderous locals. And in the supercave await far greater terrors: flooded tunnels, acid lakes, bottomless chasms, mind-warping blackness—and a cunning assassin with orders to make the mission a journey of no return.