In 2008, nine mountaineers failed to return from a winter backpacking trip in the New Mexico mountains. At their last campsite, searchers found a bizarre scene: something had appeared at the door of their tent so terrifying that it impelled them to slash their way out and flee barefoot to certain death in a blizzard. Despite a diligent search, only six bodies were found, three violently crushed and missing eyes and tongues. The case, given the code...