When a college student disappeared in Costa Rica last summer, his father — legendary Alaskan adventurer Roman Dial — went searching in Central America's deadliest wilderness. He's still looking. Early last April, a 27-year-old biology student named Cody Roman Dial set out into the remote jungle of northern Guatemala. Equipped with a crude map and a compass, he planned to traverse the Petén, a lowland rain forest teeming with snakes, illegal gold miners, and cocaine traffickers. His biggest concern, though, was dehydration — save for jeep-track mud puddles, the area lacks ready sources of freshwater. Cody had spent the previous...