In the years since, two significant clues have emerged. The first was an ice ax, discovered on the Northeast Ridge at 27,760 feet during a 1933 British expedition, and later identified as Irvine's by three parallel nicks etched on its handle. The second was Wang Hongbao's discovery of a body near the 1975 Chinese Camp VI. But despite endless parsing of Odell's account and repeated calculations of climbing rates, departure times, and oxygen use, the world knew little more about Mallory and Irvine's fate than it did in 1924.

Enter Jochen Hemmleb, a tall, stoop-shouldered geology student at Johann Wolfgang Goethe University in Frankfurt, Germany. In 1997, Hemmleb was living in a one-room flat, camping on the floor in a sleeping bag because his bed—as well as nearly every other horizontal surface in the apartment—lay blanketed in piles of old photographs, maps, and books about Everest. A climber and restless world traveler, Hemmleb had spent every spare penny since he was 16 amassing one of the largest and most meticulously analyzed private collections of Everest documents in the world. In the process, he had become obsessed by the fate of Mallory and Irvine. In 1997, after years of poring over the same historical accounts, he decided to strip away the accumulated layers of myth and speculation and to tackle the mystery as a scientific problem.

The ice ax, Hemmleb decided, was a red herring. To him the challenge was straightforward: Locate the site of the 1975 Chinese Camp VI and search an area that could be covered in the 20-minute round-trip that Wang had reported. Unfortunately, the Chinese had released little documentation of the 1975 climb. But by comparing geological background features in photographs of the Chinese Camp VI with those of other expeditions' Camp VI, lining them up on aerial photographs of the ridge, and taking a series of back bearings, Hemmleb deduced that the camp sat on an ill-defined rib of rock bisecting the snow terrace—a site far off today's beaten path to the summit.

Forget the ice ax, Hemmleb concluded. Find the camp and you'd find Irvine.

Hemmleb began publishing his findings on the Web site Everest News. On June 2, 1998, he received an e-mail message from another Everest buff, a 51-year-old American climber and publishing executive named Larry Johnson. Within a week, Hemmleb and Johnson were discussing the possibility of joining a commercial expedition to Everest's North Face and then striking out to look for Irvine themselves. Thumbing through brochures, Johnson noticed a trip run by Eric Simonson's Seattle-based International Mountain Guides—not a summit climb, but one that took clients to 26,250 feet. Johnson contacted him immediately. Simonson—a 43-year-old veteran guide who since age 18 had led some 70 expeditions, seven of them to Everest—told them that their only chance of success was a dedicated search, and the three began planning a formal Mallory and Irvine Research Expedition.

The 1924 British Everest Expedition was bankrolled with £8,000 put up by John Noel, a veteran of the 1922 British Everest Expedition, who planned to film the attempt. Simonson's team cobbled together $300,000 in sponsorship money to get its project off the ground. The 1999 team was swaddled in polypropylene and Gore-Tex. The many layers of technical wear in 1924 included, as expedition leader Edward Felix Norton wrote, "a very light pyjama suit of Messrs Burberry's 'Shackleton' windproof gaberdine" and "a pair of soft elastic Kashmir putties." The 1999 expedition recruited some of America's finest climbers: 37-year-old Dave Hahn, a senior guide on Mount Rainier who'd summited Everest via the North Face in 1994; 36-year-old Conrad Anker, a superb technical rock climber; 39-year-old guide Andy Politz, another Everest veteran; and 25-year-old guides Tap Richards and Jake Norton, who had each summited one of Everest's Tibetan neighbors, 26,748-foot Cho Oyu. In addition to Norton, Noel, and Odell, the 1924 team included surgeon and alpinist Howard Somervell and Geoffrey Bruce, who had made it to 27,500 feet in 1922. And of course Mallory, the finest mountaineer of his day, and Irvine, a second-year Oxford engineering student. The 1999 expedition took computers, digital cameras, and satellite telephones. Mallory and Irvine climbed toward the summit with at least one camera, a collapsible Kodak Vest Pocket model lent to Mallory by Somervell. Before the 1999 expedition left for Everest, Kodak technicians had said that the film, if intact, could probably be developed.