“Somebody’s been up here already,” I said.

Wood walked over and took a look at the tread marks. “Nobody was here when we showed up. And that was at five.”

“Then they were here before then.”

“What makes you think that?”

“Frost forms on clear nights, in early morning hours. Soon as the sun tops those trees, it’ll melt off, just like it would’ve yesterday, given the weather. If you got here at five, then that means they were here sometime last night.”

“How do you know we didn’t leave those tracks, backing in and out?”

I glanced at the tires on Wood’s Explorer, then at the marks left on the ground.

“The turning radius and wheelbase dimensions are different. Also, these tracks were left by smaller tires — a van or a small truck, would be my guess. Plus, you can see where the driver pulled in, put it in reverse, and headed back down the mountain.”

Wood squatted for a closer look.

“For a flight instructor,” he said, “you sure seem to know a lot about tire tracks.”

We learned all about tire tracks at Alpha, along with hundreds of other seemingly trivial topics of study. When you stalk terrorists across the globe in the name of national security, any knowledge, our instructors constantly reminded us, can become an all-powerful weapon, however inconsequential that knowledge might seem in the classroom. Tom Wood didn’t need to know all that, though.

“Tires are groovy,” I said.

He strained to laugh.

Where the pine forest was thick and the sun could not penetrate the tops of the trees, the trail was hard packed and easily negotiated. Where the trees thinned, enough so that light could filter through, the path devolved into mud. You didn’t need to be Tonto to spot two distinctly different sets of man-size footprints embedded in the brown muck. One set of prints was left by heavy-soled boots; the other, what looked like basketball or running shoes. And there was something else: to the right of the boot prints, plowed the length of the trail, were two shallow, thin gouges in the mud, spaced about a foot apart, like someone had dragged something down the mountain.

“Hikers,” Bree Kelly said as she followed me up the trail. The same two hikers, she speculated, whose tire tracks I’d noted at the trailhead, now more than an hour’s climb behind us.

“Can’t be the same hikers,” I said. “There’s only one set of prints coming back down the hill — the guy wearing the boots.”

“Could be the other guy found another way back down,” Wojewodski said, bringing up the rear. “These mountains have unmarked game trails going off all over the place.”

We stopped five minutes later for breakfast. Wojewodski offered me an apple from his pack. Wood gave me water from his CamelBak. Kelly shared a bag of trail mix. I pretended to eat the raisins, chucking them into the trees when nobody was looking. Why anyone eats dried, shriveled grapes unless they’re starving is beyond me.

The trail ascended into a narrow canyon where the sun could not go and the temperature dropped at least ten degrees, then curved northeast along a barren moraine. We traversed across talus, avoiding a modest-sized snowfield, before picking up the path on the other side and climbing in elevation. I didn’t complain when Wood stopped to check our bearings on a sun-splashed promontory overlooking Chalmers Peak and the barren granite ridge that ran south-to-north, bridging Chalmers to Mount San Marcos. I needed the rest. My legs and lungs were burning.

Wood studied the terrain ahead with a pair of scratched and dented field glasses.

“You say you saw the wreckage inside the tree line?”

I pointed. “Three hundred meters below that saddle, almost square in the center.”

We were no more than a mile from the site, Wood said. The least exhausting way to get there, he concluded, was to find a chute leading to the top of the saddle, cross the saddle to its midpoint, then make our way down the rock face and back into the pines.

“Piece of cake,” Wojewodski said, tightening the waist belt on his pack.

It was no piece of cake.

That one mile translated to a grueling, sweat-soaking, seventy-minute endurance test which probably would’ve taken considerably less time had I not lost my footing and slid about thirty feet down a sheer rock slope, twisting my football-damaged right knee and scraping up my left elbow. Wood and his colleagues had to rope me back up.

“Anything damaged?” Bree Kelly asked, checking me over.

“Only my pride.”

I stuffed the pain in a compartment deep in my brain and continued on.

“Anybody who thinks global warming is a hoax needs to come up here and have a look,” Wood said as we trudged single file behind him. “Fifty years ago, this whole area was covered with glaciers. They’re all melting, going away. Could be that’s why you saw whatever it was you saw.”

“Assuming you didn’t imagine it,” Bree Walker said.

Wojewodski spotted the debris first. The four of us had spread out line abreast, twenty meters apart, advancing slowly through the trees, when he yelled out, “Hey, I think I got something!”

I could see instantly what he’d found: remnants of a nacelle, the protective, cigar-shaped structure that protects an airplane engine. The shredded, unpainted aluminum, and what was left of the big radial engine it once housed, were wedged against a large pine and partially buried as though driven into the ground by some great force. Gouged in the earth behind the wreckage was a shallow trench twenty meters or so in length and no more than about a foot deep. This was where the nacelle had first struck the ground and been dragged along like the keel board from a sailboat before slamming to a stop against the tree. The thick blanket of pine needles that had fallen onto the trench and the nacelle, all but obscuring both from above, told me that they’d been there a long time, perhaps decades. The depth of the trench told me that the airplane to which the nacelle had once been attached had probably impacted the earth at a relatively shallow angle, as though the pilot had been flying more or less straight and level when he crashed.

Scattered to my left and similarly buried under years of pine needles, I could easily make out twisted pieces of airplane skin and frame: wing spars and ribs and what appeared to have once been an elegantly rounded wingtip.

“Hey, you guys! Hey, over here!”

I turned and saw Wood in a narrow draw, down slope, far to my right. He was waving frantically, motioning for us to come quickly. I ran as fast as my banged-up knee would allow.

There, in the shadow of the ridgeline that towered above us, partially covered over by snow and broken pine branches, was the mostly intact fuselage of a venerable, twin-engine Beechcraft, a Model 18. The empennage, or tail assembly, looked to have been sheared off.

As I approached it from the rear, I could see that the plane had come to rest on its belly, listing slightly to the left, the ground around it strewn with jagged pieces of aluminum and other debris shed upon impact. The fuselage door, aft of where the wings had ripped away when the plane went into the trees, was canted open, dangling by a single hinge. Inside the door was an open wooden crate, approximately three feet by three feet. On the ground directly outside the door was what looked to be one side of the crate. The tail number — NC1569—was evidence that the plane was more than 60 years old. Federal aviation authorities stopped adding the letter “C” to aircraft “N” registrations soon after World War II.

Through the shattered cockpit windows I gazed down at the mummified remains of the pilot, whose body was only partially decomposed thanks to the glacial conditions where his aircraft had come to rest. He was slumped forward, still strapped into the left seat. The right front quadrant of his chalky skull was missing, along with most of his front teeth — injuries that I assumed he had incurred when his face smacked the instrument panel upon impact. He’d been wearing a woolen watch cap and a double-breasted navy peacoat when he died. Both were now moth-chewed and hanging from his body in tatters. He’d also been armed. The butt of what looked like a .45-caliber, semiautomatic Colt Model 1911A protruded from the right pocket of his coat.