Before Hahn could provide him a belay, Anker was near the top of the crack. He had jammed his elbow and shoulder into the crack in an arm lock, inserted a foot and leg into it below, and hoisted himself up. Now he needed to move right, around an overhang. There was a perfectly positioned narrow ledge to make this move possible, but one of the ladder rungs was in the way. He reached to the right, got a firm handhold on the rock face, and pulled across, placing his foot on the rung that blocked the ledge. A few moments later he was at the top of the Second Step. "I was able to knee-bar to the top," he said, "and got a size three Friend [a spring-loaded cam device] at the top of it and then got a hand jam into the crack. I got the Friend in, and then I had to step out." Anker did not end up using the protection he placed, and his brief reliance on the ladder would have been unnecessary had it not been in the way. Anker rated the climb 5.8, adding that at such a high altitude, without oxygen, it felt like 5.10.

By radio, Simonson asked the big question: "Could Mallory have scaled the headwall?" Anker replied that he thought Mallory could have negotiated it—albeit with difficulty. (He has since declared that it's unlikely.) As for Hahn, "There is no question in my mind that an accomplished climber could have climbed that headwall with no aids, and we know Mallory was an accomplished climber. But what I wonder about is the combination of factors. Could they have done it all? In 1924, when the route was unknown? I don't know."

What modern adventurers tend to forget is that early mountaineers had to rely on considerably more grit to pioneer high-altitude exploration in the first place. Look at them, we say; they were so ill-equipped, their oxygen apparatus so primitive, their clothing so appallingly inadequate. But ultimately success on Everest has less to do with either technical skill or modern equipment than with sheer brute strength, guts, and, not incidentally, good weather. And a close reading of the formal expedition reports from that period reveals that these men climbed with remarkable speed, skill, and ease despite often dreadful conditions. They pioneered routes, established camps at sites still used today, and equaled or beat today's climbing rates, often without supplemental oxygen. Mallory, of course, was the best of them all; by all accounts he climbed both with the agility of a cat and with an incredible eye for route-spotting.

Whether they were on the Second Step or the Third Step when Odell saw them, it is clear that Mallory and Irvine had made excellent progress. At this point, there were three pressing issues that they had to deal with on their way to the top: weather, oxygen, and time. Despite the brief squall that hit Odell at Camp VI, it was not storming on Everest that day, and that night was clear and calm. As for oxygen and time, if cylinder No. 9 was emptied between 8:45 and 9:15 a.m., the next cylinder at full flow would have been depleted sometime between 12:45 and 1:15 that afternoon, the very time Odell saw them moving so quickly. There are only three explanations for their speed: They were unbelievably strong despite having run out of oxygen; they had been climbing at less than full flow and so had not yet run out of oxygen; or they had each switched to a third, fresh oxygen cylinder.

If the climbers had carried only two cylinders each, they would now be faced with a terrible dilemma—either abandon the summit and descend immediately to safety, or continue climbing without supplemental oxygen. If they continued, they almost certainly couldn't have reached the summit until around 7 p.m. Even if they turned around immediately, they would not have had enough time in the remaining hour and a half of dusk to descend the summit pyramid, much less the Second Step. Having left all their lighting gear at Camp VI, the two climbers would have had to rely on starlight to see anything. The moon, only a sliver on this night, set shortly after 11 p.m. Simonson and other Everest veterans agree that it is impossible to climb down the Second Step in the dark.

But Mallory's body was found below the Yellow Band, north of the First Step, not the Second. So he must have come down the step in daylight or dusk. If Mallory and Irvine had turned back immediately when their second cylinder of oxygen ran out, they would have been back at Camp VI sometime later that afternoon, while it was still daylight. Yet if Mallory was descending in broad daylight when he fell, why were his sun goggles in his pocket, when he had seen Norton, his own expedition leader, struck snowblind just two days before? Either the altitude had rendered Mallory both clumsy and stupid, or he and Irvine did not turn back when their second bottles ran out. If so, they must have each had a third cylinder.

Driven on by the realization that the summit was at last within their reach, though no doubt climbing more slowly than they had earlier in the day, Mallory and Irvine could have reached the summit by 5 p.m., just finishing their third oxygen cylinders. By this scenario, and only this scenario, would they have had time to descend through the Second and First Steps with sufficient daylight and have ended up in the Yellow Band in darkness.

Without a definitive snapshot from the famous Kodak Vest Pocket camera, of course, we will still never know if they reached the summit. Yet there is one especially tantalizing, if indirect, clue that they may well have made it. Mallory intended to place a photograph of his wife, Ruth, on the top of Everest. But no photograph of Ruth Mallory was found on his body. Where is her picture, if not at the summit?