LIKE A SLITHERING SNAKE INDEED  thought Skip, as he adjusted the tiller and guided the little dinghy around one more turn, to the right this time. On the map, the river looked more like some long, twisted worm, an internal parasite of some sort.

This new river, much narrower than the Madre de Dios, had become an endless series of twists and bends, in an annoyingly regular pattern, every hundred yards or so. Right, left, right, left, and on and on. It reminded Skip of a mountain highway he'd driven once, in Northern California, across the Coast Range from Eureka over the hills to the Central Valley. It was the only time he'd ever felt carsick.

Despite the monotony, there was a certain zen to it. Even the drone of the motor was soothing, putting one at peace with the surroundings. Skip leaned back and felt the sun on his face and breathed deep of the dank air, rich with the smells of earth, jungle and water. Looking back down to line up yet another turn, a school of small fish passed as a shadow just below his right elbow, which was leaning out over the tube. Piranha? There were dangers here, always. That run-in with the anaconda was a reminder of that. But at times like these, he felt alive and in his element.

He rested his eyes on his son, Zane, and wife, Nusiri, both with genetic connections to this land. Not your average family vacation, now was it? And it sure beat running a river guiding a bunch of tourists, no matter how well that had paid. Yes, this was the best of both worlds, family and adventure.

A sudden flurry of motion, low on the water, brought his attention over to the right bank. Yep, piranhas, all right. No telling what they were feeding on. Skip was just glad it wasn't him or anyone else. But he was thankful for the distraction, for he saw the little stream coming in from over there. The first landmark he was supposed to be looking for, while his mind was elsewhere. If not for those hungry little fish, he might have missed it, and by extension, miscounted the next tributary, the one he needed, as the first instead of the second. It would not do to take a wrong turn in a wild country such as this.

It took another two long hours before be found the next river that he was looking for. More of the same awaited them here: endless winding river, narrower still, with the forest canopy close in some places and open sky in others, and the travel easy against the slow-moving current. Skip began to take notice of just how far into the wild they were. The last trace of human habitation was early this morning, just an hour or so into the journey. Out here their only company was macaws and monkeys, capybara and an occasional caiman, and all the rest of the critters of the Amazon rainforest. In his younger days, Skip would revel in being so deep into the wilderness. The further out, the greater the adventure. Now, seeing through the eyes of a middle-aged-and-counting family man, he began to notice how truly isolated they really were. Everything he held dear was packed into this little inflatable dinghy. Not for the first time, he wondered: what had he gotten them into?

He glanced to the sky and saw that they were catching up with the thunderclouds he'd seen earlier. He slowed the boat a bit and called ahead to Zane and Nusiri. "You might want to put on ponchos. We've got rain coming in, in just about...seven and a half minutes."

True to his prediction, plus or minus five seconds, the heavens opened up, drenching them, but providing a refreshing respite from the tropical sun. The tradeoff, of course, was the amplified humidity fifteen minutes later, when the squall had passed. As the clouds moved on and the sun again beat down, they shook off and stowed their ponchos, bailed out the rainwater that had built up on the floor of the raft, and continued on their way.

It was later that afternoon, after they'd made the left turn to the next river on their route, that things began to get interesting. At least this time the split took them up the wider of the two streams.

First, while they were still in the flats, came the maze of braided channels that wound around little wooded islets where the two forks of the river converged. More than once, Skip followed what appeared to be the main channel, only to find a dead end on the back side of an island, having to come about, backtrack and start again. A couple of times, he pulled into a cove, got out and climbed a tree to get a better view and check his bearings. In several places the river, bending full circle back on itself, through years of erosion, cut a new channel, leaving the far end of the curve isolated as an oxbow lake. He was having a newfound respect for Fawcett and the other early explorers who had braved this convoluted landscape.

Then, as they finally began to move into the foothills of the Andes, the pace of the current they were traveling against picked up in proportion to the rise in elevation. Skip was glad now for that new, more powerful motor.

He was no stranger to river running, but that had been years ago, in a more flexible raft built for swift water, with self-bailing construction, and paddling downstream, not motoring up against the current. At first, it was a matter of just applying a bit more throttle to counter the increased speed of the water. But then skip found himself among giant boulders, having to read the river to determine the best way around. He gunned it to get up a wide chute between two big rocks, hoping all the while that the water was deep enough for the prop to clear whatever might lie beneath the surface.

The bow caught air as they made it over the top, Zane whooping for joy. Nusiri was holding onto the side grab rope with a death grip. Spray flew to the sides as the bow came back in contact with the water, but by then, Skip was already lining up the next maneuver, a hard turn to port around another set of boulders, aiming for the eddy formed behind. He was glad for the V-shaped inflatable keel that gave him stability and maneuverability.

And now they had to contend with a long field of rifles and rolling waves. Skip took each wave head on, almost jumping over, with the bow flying up and over, then nose down into the trough, then back up again, repeat. Zane, riding the bow, was having the time of his life. Skip, flashing back to when he was that age, suddenly thought of it in dirt-bike motorcycle terms. This was the nautical version of whoop-de-doos on a motocross course.

As the whitewater midstream became impassable, Skip looked for the eddies on the inside of the turns to keep them going. Trying to shoot cross-current, he momentarily got them sideways.

"Hold on, we're going over!" he shouted, even as he turned the tiller for all it was worth to get them facing the right way.

The raft listed heavily to starboard. All three of them threw their weight to port to counterbalance.

A wave hit them at just the right angle to lift the bow high, diagonally, and then twist the whole craft back around and down.

All three bodies hit the floorboards as the dinghy slapped the water in what amounted to a hard belly flop.

Skip grabbed the tiller again and swung them back on course.

Around one more tight bend, up one more chute, and then they were home free, in a wide, deep pool. Up ahead the river continued on in a long bend to the left. The bank on that side was a tangle of jungle thickets. To the right was a line of cliffs at least a hundred feet high. Near the top, a waterfall issued from the edge of a V-shaped hanging valley. A fine curtain of mist draped the top of the waterfall, carried away by a gentle breeze.

Skip swung the boat around so that they were facing it, then cut the motor to idle, holding them steady. He looked up at the waterfall and the steep valley it came from. He hurriedly checked his map and the journal.

"This is it," he declared, pointing up at the hanging valley. "That's the 'Notch.' It's gotta be."

He turned the boat to shore, landing on a beach of mixed rock and sand, opposite the falls.

"It's getting late in the afternoon. We'll camp here tonight. Tomorrow, we'll have to find a way up there, climb up past the falls. This is as far as we can go by boat. It's a long trek from here, up that valley and into the mountains."

Zane had his eyes on the waterfall too, but with a strange expression on his face.

"There are spirits there," he said. "Spirits in the mist."