I don’t hear what Stone hears, but the black trough beneath us bears steadily left, and my forward line of sight has gone black. Then, slowly, the sound registers on my traumatized eardrums, like holding my ear to the biggest conch shell in the world. Fear balloons in my chest, pressing my heart into my throat.

I don’t think Stone’s paddle is affecting the course of the boat anymore. I feel like I’m trapped in a roller coaster as it tops its highest incline and tips slowly forward, headed for the long vertiginous fall. On both sides, walls loom out of the dark, near enough to touch.

Then we are airborne.

“Lean back!” yells Stone as the kayak is hurled forward into space. I obey out of pure instinct, my stomach flying up my throat as the bow plummets down a thundering pipeline of water and smashes into something I cannot see, then bounces up into a roiling mass of foam and spray.

“We’re clear!” he cries. “One down!”

We’re back in the main current, riding as smoothly as a subway car on a scheduled run. The walls of the canyon have fallen away, and the sky above us has widened into a starry blanket that gives the snowy riverbanks a silver sheen.

For ten minutes we slide along as though on a Nile cruise, but every so often a stand of spruce near the river’s edge reminds me just how fast we are moving. The farther we go, the more the valley widens around us, until it seems we are floating across a vast desert of snow. On another night this might seem an ideal time for Stone and me to talk, for him to tell me what to watch for ahead, or to discuss the eternal subjects like women and time. But tonight all we can do is shiver in the wind, chilled so deeply that if we don’t find warmth and shelter soon, we could die from exposure.

Almost without our noticing, the banks begin to rise again. It feels like the river is cutting its way into the earth, carrying us with it on its darkening journey. The sound of the turbulent water grows as the walls rise, like the sound of a great beast waking from a long sleep.

“It’s coming,” Stone says from behind me. “Listen.”

Only the center of the stream is smooth now, a black torrent rushing through the narrow canyon, throwing off a mist of silver froth and spray. The kayak hurtles down this black tunnel like it’s on rails, but of course it’s not. If the bow gets turned around, we could spin out of control and be smashed on a rock, or capsize and be pinned by an inescapable hydraulic.

“Lean right!” Stone yells.

The kayak’s nose pulls left, then slingshots around a bend, its fabric skin scraping the rock wall with a resilient wail.