IT WAS A CLEAR Labor Day morning when Steve Fossett told his pal Barron Hilton-whose million-acre Flying M Ranch, near Hawthorne, Nevada, he was visiting-that he was going for a spin. He took off at just before 9 a.m. in Hilton's Bellanca Super Decathlon, an athletic high-wing designed more for aerobatics than any long-distance flying. The plan was to be back for lunch. A soybean tycoon from Chicago, Fossett could take care of himself; the man was the first to pilot both a hot-air balloon and a jet around the world; he'd swum the English Channel, mushed the Iditarod, and finished the Ironman Triathlon. But when he didn't come back by nightfall, Hilton and Fossett's wife, Peggy, launched what would become the largest and most expensive search-and-rescue operation in American history, one that would ultimately eat up $1.6 million in public and $1.2 million in private funds.

For more than a month, the search dragged on. They went big: Civil Air Patrollers blanketed the desert and subalpine sky. Walker Lake, the only big blue spot anywhere near the ranch, was seined with high-tech electronics. Expensive high-resolution photographs were fed into computers looking for anomalies. Meanwhile, amateur geeks from Switzerland and New Zealand looked for Fossett's plane on their coffee breaks, via Google Earth. But on February 15, 2008, after the ATVs and the satellites and the dogs and the geeks turned up nothing, the 63-year-old adventurer was declared dead.

The mystery, however, was in full swing. Conspiracy theories were fermenting: Fossett had faked his disappearance; his financial ship was taking a nosedive. Fossett was only very recently "checked out" on that particular aircraft, not an easy one to fly. There's debate over whether or not the plane was topped off with fuel. The Flying M staff pilot was the only one who saw him take off, then-maybe-a cowboy saw him south of the runway. But where was he going? And why didn't the emergency transmitter go off?

Into this cloud bounded Simon Donato in a pair of Merrell trail runners. His plan: to use hyperfit dudes on the ground, where technology turned up nil. A stratigrapher by day, making his living mapping layers in the earth for oil exploration, Donato is also a veteran adventure racer, his résumé stuffed with sufferfests from Eco Challenge Fiji to Raid the North Extreme, Newfoundland. His idea, dubbed Adventure Science, is that with their superior fitness and endurance, adventure racers are ideally suited to canvass vast and rough country that turns back 4x4s and ATVs-and in a tenth of the time it takes classic foot searchers. "I had an epiphany several years ago while conducting my geology Ph.D. field work in Oman," Donato says. "I realized that doing things 'the easy way'-i.e., driving instead of walking-sometimes meant that crucial details were overlooked. Obviously, the high-tech method to find Fossett has failed, so it only makes sense to put the fastest and fittest people I could find on the ground to search the most difficult areas."

The Fossett search is a test run. Donato has plans to use Adventure Science to look (at high speed) for dinosaur bones in Alberta next summer and to search (at peak fitness)for lost Inca cities in Peru. He explains this all on adventurescience.ca, which looks not unlike a movie trailer-"The adventure begins July 14..."-and reads like a thriller:"They will pack lightly, move quickly, and suffer extremes. They will explore the unexplored."

Donato, however, wasn't alone in thinking that it might take an adventurer to find an adventurer. Robert Hyman, a Washington, D.C., alpinist and Explorers Club fellow (Hyman and Donato are both members, as was Fossett) was planning a search trip for August-a self-funded undertaking with ATVs that would also test "search-planning visibility software"for NASA. Hyman, a 49-year-old private investor, told me he believed that the wreckage was in "the vertical zone," maybe hidden under a cliff or slammed into a rock cleft, and that he'd recruited several elite climbers, Wyoming-based Exum Guides Michael Ruth, Wes Bunch, and Calvin Hebert. Unlike Team Adventure Science, Hyman had the blessing of Fossett's family.

The expeditions, however, were cooperating, and both had the seriousness of purpose, Hyman emphasized, of locating a presumed dead colleague. That's not to say there wasn't a little polite trash talk. "I checked out Donato's Web site. It sure seems like he's using the Fossett name to promote himself," Hyman emailed me. "But I hope they find the crash site."

So did I. I have to admit, though, I arrived in the desert a skeptic. If millions of dollars and an arsenal of Space Age technology couldn't find a multimillionaire in an airplane, how were a bunch of Canadian marathoners with Band-Aids on their Lycra-chafed nipples going to pull it off?