Just as the gray disk that was the sun climbed to the day’s zenith, Seth heard the pitch of Gunther’s snowmobile drop suddenly. The sound was followed immediately by the brake lights of the second machine. Seth gripped the brakes on his own snowmobile’s handlebars and squeezed them to a stop.

Wordlessly, they dismounted and helped to pull the supply sled toward the mouth of the mine.

In a matter of minutes they dragged the sled into the shelter of a rock overhang. Ahead of them an iron gate barred their entrance to the mine. Gunther pulled the tarpaulin from the sled and began to pass around the equipment. To Seth, Zoe, and Stratton, he handed backpacks that weighed about twenty-five or thirty pounds. He handed all of them flashlights and whistles with a lanyard. “Wear these around your necks at all times,” he told them. “If you get separated, stay in one place and blow on the whistle.”

He slung a large coil of climbing rope diagonally over one shoulder, then buckled a beltload of carabiners and pitons, as well as a hammer to drive the pitons, around his waist.

“The rock entrance to this mine is very unstable,” he told them. “Once we hit the salt, everything will be fine. But the rocks and the shorings that compose the first four hundred feet of the tunnel are in danger of collapse.” And, as if to confirm Gunther’s gloomy diagnosis, a scattering of rocks clattered somewhere in the darkness beyond.

“There is a vent hole cut vertically into the upper portion of salt. If the entrance is blocked, we can work our way out using the climbing gear.” He walked up to the iron gate, unlocked a remarkably battered padlock, and swung the gate open. They followed him in.

The impoverished light penetrated only the first fifty feet or so of the mine entrance. Everyone had turned on their flashlights. Still, the going was treacherous, with ice underfoot and great stiletto-like stalactites of ice suspended from the ceiling.

Seth and Zoe walked cautiously along the icy floor, daring to take only small steps as the floor of the mine sloped inexorably downward. Remnants of the pitiful daylight vanished entirely now in the great blackness of the tunnel. To conserve batteries, Gunther ordered everyone but him to turn off their flashlights. His light picked out rotten wooden shorings and the rusty remains of metal ones. It was apparent that the rock faces above and to either side of them hung there against gravity with no support at all. Seth wanted to ask Gunther about that, but didn’t He didn’t really want to know the answer.

Suddenly the sounds of falling rocks filled the tunnel. Somewhere in the darkness, not too far beyond the bright cone Gunther’s flashlight carved out of the darkness, came the dull hollow clattering of stone against stone.

“Wait,” Gunther said in a hushed voice. He had warned them earlier not to make loud noises. The rocks in this portion of the mine were so poised for a cave-in, he said, that any loud noise might be enough to trigger a collapse. His warning had a chilling effect on any conversation, loud or otherwise. He, after all, was the man who had worked in the mines all his life. The sound of falling rocks continued for several seconds. The tunnel floor vibrated under their feet, and instants later small rock fragments began to fall around them from the tunnel ceiling.