THE OMO'S MOST CHALLENGING RAPID, about 175 miles below the put-in, is called Tis Isat ("Smoke of Fire") Falls South. When we pulled over to scout the drop, on day nine, we were a slightly different team. Tom Bateman, our sharp-witted management professor, had left after an old foot injury flared up. We'd picked up photographer Liz Gilbert and a sweet Greek tourist named Simoni Zafiropoulou. A tall, middle-aged blonde who favored flamboyant jewelry, she'd met us at our hotel in Addis and, to everyone's shock, popped up at the resupply bridge, carrying her clothing in garbage bags. She was desperate to join the team. What could Scaturro say?

Scaturro consulted a sketch of the rapid in his 2001 river log, taking careful note of a keeper hole that couldn't be seen from where we stood. He warned the other boatmen. Liz said she wanted photos of the other rafts in the rapid. No problem, Scaturro said. He would eddy out at the bottom of the run, after clearing the hole.

Simoni, Liz, and I sat in the bow of Scaturro's boat, while Yalew lounged on a pile of drybags lashed to the stern. Scaturro told us to crouch in the bilge and hold tight to the grab lines. Straining at the oars, he ferried across the channel, pivoted downstream, and let the river do the rest. The boat bumped and crunched over rocky shoals, hung up briefly, then continued sweeping down through the left-trending curve. Scaturro was standing at the oars, making minor course corrections, when he glanced sideways to scope out the best way into the eddy. When he looked back, he screamed, "Hold on! Hold on!" He'd forgotten about the keeper hole.

I was on the raft's downstream side, which plunged into the hole first and slammed into a standing wave. A wall of water crashed over my back. The boat tilted at a steep angle as backwash drove the downstream tube underwater. A weird roaring sound filled the air. We were trapped and about to flip.

Instinctively, Scaturro dropped the oars and moved to the high side. "Get in the back of the boat!" he yelled. "Get in the back!" He grabbed Simoni and Liz by the scruffs of their life jackets and yanked them into the middle of the raft.

Suddenly weightless, the bow popped up and leaped over the backwash. We were all right.

Scaturro looked shaken. Our close call was a disturbing flashback to near misses that he'd vowed would never happen again. One had occurred about a month into the Nile expedition, in the river's ominous Black Gorge.

In Gordon Brown's retelling of that 2004 episode, he was scouting in his kayak and ran a long rapid with a 12-foot pour-over that couldn't be seen from upriver. Scaturro followed in his raft, but a mixup in signals sent him careering over the drop into a nasty hole. Scaturro threw himself on the raft's high side to prevent it from flipping. He washed out of the hole, but the raft following him, piloted by Chilean photographer Michel L'Huillier, a whitewater novice, dropped into the pit sideways and capsized, pitching everyone aboard into the river and nearly drowning the trip's cook.

The Imax movie shows L'Huillier's flip but not the subsequent shouting match between Brown and Scaturro. The two got into it as the rattled Ethiopian camp staff looked on. Scaturro said he didn't see Brown's signals; Brown thought Scaturro had ignored them. When Brown accused Scaturro of being reckless with people's lives, he touched a nerve. Two of Scaturro's teammates had perished on previous expeditions, both in 1993: climber Greg Gordon, who slipped to his death on Pumori, the 23,494-foot peak next to Everest; and Harriet Nicholson, the fiancée of one of his clients, who drowned on a rafting holiday on the Yukon's Alsek River. Nicholson's death was especially troubling, because she'd been riding in Scaturro's boat, which flipped in a deep hole that he saw too late. Years later, the deaths still haunt him.

Our near miss at Tis Isat happened for the same reason as the Alsek accident. "In both instances," Scaturro says, "I was paying attention to other things rather than concentrating on the river, something I try never to do, but it does happen."

Tis Isat hadn't quite finished with us. The moment we reached shore, we heard a piercing emergency whistle. Scaturro grabbed two throw bags of coiled rescue line and dashed upriver, hopping across the sharp, black boulders in his flip-flops. It was only a false alarm: one man briefly overboard.

"I need a rest," Scaturro said afterwards. "I need lunch."

Petros didn't take the hint.

"Petros, lunch!" Scaturro hollered. "I am still the goddamn expedition leader, and I want lunch."

That night in camp, perhaps to make a point to Petros, he handed napkins to everyone after dessert. Five minutes later he was fast asleep, slumped in a chair by the campfire with his chin on his chest.