I hear Mack screaming my name. The terror in it seems to silence my fear enough that I reach out and grab for anything to stop my fall.

Suddenly, I’m plummeting past a piece of the rock wall big enough for me to close my hand around. I grab it.

I spend the next few seconds scrabbling with my other hand for another place to hold on to. But I find a handhold, and then I spend several more seconds moving first one foot, and then the other looking for a place to wedge my feet.

When I feel ...