BEFORE A STORM, CLIMBERS always sense tension. The changing weather charges the atmosphere with a last-chance sort of feeling. On August 17, the sixth day of captivity, clouds fill the sky. The temperature is near freezing, the air damp. Something's brewing. Before dawn Abdul returned with two stinking, greasy 40-pound sacks. One contains salty yak butter, the other balls of congealed yogurt—Abdul and Su, as desperate and starving as their charges, start in on the provisions, most likely taken from a farmer. The Americans each force down one or two of the rancid balls. In his bivvy cave Smith sits on the suitcase-size slab of butter, insulation against the cold rocks. For the first time in a long time, Caldwell prays.

At dusk they get under way again. Abdul explains that they must climb the rugged west side of the Kara Su Valley to a plateau 3,000 feet above. There they will rendezvous, waiting several days if necessary, with Abdullah and Obert—who the Americans think must be dead, judging from their radio silence these last two days and several distant bursts of fire. Eventually they will be taken north, to Uzbekistan, the hostages are told.

Then Abdul turns away, signing that he will catch up after he heads up to the Americans' base camp, where the stashed duffels hold fresh radio batteries. It is 10 p.m. From where they stand, at the foot of a perilously steep climb that they'll have to tackle without ropes, it is an hour to base camp, an hour back. Su is now their only guard; the hostages will have most of the night alone with him. As they begin to climb the succession of slabby cliffs and steep grassy slopes, Dickey turns to his companions and says, "We gotta whack this guy, tonight."

Stifled by rain clouds, the now full moon rounds the mountainside and bleeds onto the group as it reaches a point 2,000 feet above the river. The Americans and their guard climb a moderately difficult rib, a series of 5.2 pitches, flanked by glacier-carved cliffs. Smith and Dickey shadow Su the whole way, openly talking about finding a place to push him off. But they are each burdened with the heavy bags of butter and yogurt balls, and Smith has Turat's sleeping bag draped clumsily around his shoulders, like a shawl.

"We had all been talking about killing someone for days," Caldwell will remember, clearly uncomfortable with the memory, "but Beth had said to me she just didn't think I could emotionally handle it. So I was staying out of it."

"Alpinista!" Su orders Smith to the front. He waves his hand at the cliff as if to ask, "Which way?"

Smith heads up the 60-degree face, pointing out the handholds to Su, urging him on like a guided client. Su slings his AK-47 over his shoulder and scrambles up. A shove here would be fatal, and Smith steps into position to body-slam Su off the ledge. But the rebel skirts around him, oblivious, and starts up another step of rock.

"OK, this is it," Dickey says in a trembling voice. He hands Smith the sack of yogurt balls and climbs into position, just below Su.

"Come on, do it, John," comes a collective murmur out of the night. But Su moves beyond Dickey's reach. It is now midnight. They are near the top of the last cliff. Somebody has to do something.

Caldwell is thinking his friends might not do it. And he starts worrying about how they would survive a storm up here, worrying about Beth, wondering what will happen to them all in Uzbekistan. He turns to Beth and asks, "Do you want me to do it?" She doesn't say anything. Then he starts moving toward Su.

Fueled by a wave of adrenaline, Caldwell scrambles across the ledge and up the cliff. He reaches up, grabs the rifle slung over Su's back, and pulls. A faint breath of surprise, a sound like whaaa, escapes Su's lips. He is falling.

The rebel arcs through the circle of the moon, pedaling air. The climbers see him hit a ledge 30 feet down with a crack. Then Su rolls off into the darkness, over the 1,500-foot cliff to the river below.