“This doesn’t look good,” Seth Kantner muttered, peering at the pale gray end of a spark plug, then passing it to Vic Walker and me for inspection. The top plug on my side looked even worse—grains of aluminum piston speckling the electrode, sure signs of a damaging, possibly fatal, engine overheat. My jet skiff lay against a cut bank up the Nuna River in northwest Arctic Alaska on a fading September evening. Globs of icy rain hissed on the still-hot engine. At the very least, we were bound for a three-mile slog over swampy, slush-coated tundra to Seth’s cabin, and after that, a chain of logistical headaches trailing over the horizon, featuring a crippled skiff far from home. It was one thing if an impossible-to- dodge boulder or a twitch of fate had caused the mess. But none of it had to happen. I had three rapid-fire chances to avoid…