Once again it is the knife that saves me. I plunge the blade into the ice while the tree drifts away. The point scrapes, then sticks.

My legs swing downstream, the toes of my boots appear before me. For an instant, I am like a sea otter reclining on his back. I am terrified I will lose my grip. So I reach up and get two hands on the knife handle and begin kicking furiously. When my chest touches the edge of the ice, I do my best to pull myself up, hoping the blade sticks.

I manage to get my elbows onto the flat surface. I bring up one knee to get a purchase only to hear a sharp crack. The ice, which can’t be more than three inches thick, is breaking like china under my weight.

I lift my other leg clear of the water and roll onto my back. My teeth chatter uncontrollably.

It seems I’m on another ice floe. This one is larger, the size of a barn door, but not buoyant enough to keep me afloat. Water streams over its opaque surface as it begins to sink beneath me. I lunge onto the adjoining sheet and, this time, keep moving. I crawl on hands and knees, listening for the cracks that foretell a collapse.

I am nearer to the eastern bank than the western bank where I plunged off the road. Forty-degree water moving at two thousand cubic feet per second separates me from safety. I have no choice but to continue on, to the unknown shore.

The snow, light and dry from the crispness of the night, flutters more than falls.

Movement downstream catches my eye. Amazingly, it is Shadow. The black wolf is bounding across the ice and in three leaps gains the eastern shore.

My wet face hardens into a mask as I climb to my feet. Now I hear the cracking sound familiar to any skater who’s tested a frozen pond for the first time.

I leap forward, then leap again, somehow keeping my balance. My flash-frozen clothes make rubbing noises as I move. Suddenly the world lurches beneath me. I have stepped onto yet another floating plate.

I have no time to think. My foot goes through a soft, slushy spot and I nearly lose my boot in the hole, but I am inspired by the sight of the wolf and full of fresh resolve, and I keep going, until I find myself standing on something that feels like land. It is the laminated ice that has built up, over the course of subzero nights, along the river’s edge.